Becker's muscular dystrophy: Difference between revisions

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{{CMG}}; '''Associate Editor(s)-in-Chief:''' Moises Romo, M.D.
{{CMG}}; '''Associate Editor(s)-in-Chief:''' [[User:MoisesRomo|Moises Romo, M.D.]]


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== Overview ==
 
Former "[[pseudohypertrophic muscular dystrophy]]", now Becker's muscular [[dystrophy]], is a [[Genetic disorder|genetic]] [[neuromuscular]] condition characterized by slowly progresive [[Muscle weakness|weakness]] and [[atrophy]] of [[Skeletal muscle|skeletal]] (mostly legs and pelvis) and [[cardiac muscles]].
== Overview[edit | edit source] ==
Former "pseudohypertrophic muscular dystrophy", now Becker's muscular dystrophy, is a genetic neuromuscular condition characterized by slowly progresive weakness and atrophy of skeletal (mostly legs and pelvis) and cardiac muscles.<ref>{{Cite web|url=https://medlineplus.gov/ency/article/000706.htm|title=Becker muscular dystrophy|last=Campellone|first=Joseph V.|date=02/27/2018|website=Medline Plus|archive-url=|archive-date=|dead-url=|access-date=05/24/2020}}</ref> It is a kind of dystrophinopathy inherited in an X-linked recessive fashion.<ref>{{Cite web|url=https://rarediseases.info.nih.gov/diseases/5900/becker-muscular-dystrophy|title=Becker muscular dystrophy|last=|first=|date=05/01/2020|website=Genetic and Rare Diseases Information Center|archive-url=|archive-date=|dead-url=|access-date=05/24/2020}}</ref>


== Historical Perspective[edit | edit source] ==
== Historical Perspective ==
Becker's muscular dystrophy was first described by Peter Emil Becker, a German neurologist, psychiatrist and geneticist, in 1953 with his thesis called ‘‘Dystrophia Musculorum Progessiva: A Genetic and Clinical Investigation of the Muscular Dystrophies’’, after his work was interrumpted in 1942 due to WWII recruitment.<ref name="pmid23576413">{{cite journal| author=Zeidman LA, Kondziella D| title=Peter Becker and his Nazi past: the man behind Becker muscular dystrophy and Becker myotonia. | journal=J Child Neurol | year= 2014 | volume= 29 | issue= 4 | pages= 514-9 | pmid=23576413 | doi=10.1177/0883073813482773 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23576413  }}</ref> 


Before Becker, in the 1860's, French neurologist Guillaume Benjamin Amand Duchenne described in detail a slowly progessive muscular weakness in a boy, later known as Duchenne muscular dystrophy.<ref>{{Cite web|url=http://www.whonamedit.com/doctor.cfm/950.html|title=Guillaume Benjamin Amand Duchenne de Boulogne|last=Kleinert|first=Rudolph|date=|website=Who named it?|archive-url=|archive-date=|dead-url=|access-date=05/25/2020}}</ref><ref name="pmid31789220">{{cite journal| author=Mercuri E, Bönnemann CG, Muntoni F| title=Muscular dystrophies. | journal=Lancet | year= 2019 | volume= 394 | issue= 10213 | pages= 2025-2038 | pmid=31789220 | doi=10.1016/S0140-6736(19)32910-1 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=31789220  }}</ref>
* Becker's muscular [[dystrophy]] was first described by Peter Emil Becker, a German [[neurologist]], [[psychiatrist]] and [[geneticist]], in 1953 with his thesis called ‘‘Dystrophia Musculorum Progessiva: A [[Genetic]] and Clinical Investigation of the Muscular Dystrophies’’, after his work was interrumpted in 1942 due to [[World war|WWII]] recruitment.<ref name="pmid23576413">{{cite journal |vauthors=Zeidman LA, Kondziella D |title=Peter Becker and his Nazi past: the man behind Becker muscular dystrophy and Becker myotonia |journal=J. Child Neurol. |volume=29 |issue=4 |pages=514–9 |date=April 2014 |pmid=23576413 |doi=10.1177/0883073813482773 |url=}}</ref><ref name="urlGuillaume Benjamin Amand Duchenne de Boulogne">{{cite web |url=http://www.whonamedit.com/doctor.cfm/950.html |title=Guillaume Benjamin Amand Duchenne de Boulogne |format= |work= |accessdate=}}</ref>
* Before Becker, in the 1860's, French [[neurologist]] [[Guillaume Benjamin Amand Duchenne]] described in detail a slowly progessive [[Muscle weakness|muscular weakness]] in a boy, later known as [[Duchenne muscular dystrophy]].<ref name="pmid31789220">{{cite journal |vauthors=Mercuri E, Bönnemann CG, Muntoni F |title=Muscular dystrophies |journal=Lancet |volume=394 |issue=10213 |pages=2025–2038 |date=November 2019 |pmid=31789220 |doi=10.1016/S0140-6736(19)32910-1 |url=}}</ref>
* The association between [[genetic mutations]] and Duchenne [[muscular dystrophy]] was made in 1986.<ref name="HoffmanBrown1987">{{cite journal|last1=Hoffman|first1=Eric P.|last2=Brown|first2=Robert H.|last3=Kunkel|first3=Louis M.|title=Dystrophin: The protein product of the duchenne muscular dystrophy locus|journal=Cell|volume=51|issue=6|year=1987|pages=919–928|issn=00928674|doi=10.1016/0092-8674(87)90579-4}}</ref>
* In 1987, [[dystrophin]] gene on [[X chromosome]] were first implicated in the [[pathogenesis]] of Becker's [[muscular dystrophy]].<ref name="HoffmanBrown1987" /><br />


The association between [[genetic mutations]] and Duchenne [[muscular dystrophy]] was made in 1986.<ref name="pmid3319190">{{cite journal| author=Hoffman EP, Brown RH, Kunkel LM| title=Dystrophin: the protein product of the Duchenne muscular dystrophy locus. | journal=Cell | year= 1987 | volume= 51 | issue= 6 | pages= 919-28 | pmid=3319190 | doi=10.1016/0092-8674(87)90579-4 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=3319190  }}</ref>
== Pathophysiology ==


In 1987, [[dystrophin]] gene on [[X chromosome]] were first implicated in the [[pathogenesis]] of Becker's [[muscular dystrophy]].<ref name="pmid33191902">{{cite journal| author=Hoffman EP, Brown RH, Kunkel LM| title=Dystrophin: the protein product of the Duchenne muscular dystrophy locus. | journal=Cell | year= 1987 | volume= 51 | issue= 6 | pages= 919-28 | pmid=3319190 | doi=10.1016/0092-8674(87)90579-4 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=3319190  }}</ref>
* The [[pathogenesis]] of Becker's muscular [[dystrophy]] is characterized by muscle [[Muscle weakness|weakness]] and [[pseudohypertrophy]] (mostly [[proximal]]), [[Hypertrophic cardiomyopathy|cardiomyopathy]], elevated [[CK]] and skelletal [[Deformity|deformities]].<ref name="SarkozyBushby20143">{{cite journal|last1=Sarkozy|first1=A.|last2=Bushby|first2=K.|last3=Mercuri|first3=E.|title=Muscular Dystrophies|year=2014|doi=10.1016/B978-0-12-801238-3.05597-5}}</ref>
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* Becker's muscular dystrophy is inherited in an [[X-linked]] recessive fashion.<ref name="urlBecker muscular dystrophy | Genetic and Rare Diseases Information Center (GARD) – an NCATS Program4">{{cite web |url=https://rarediseases.info.nih.gov/diseases/5900/becker-muscular-dystrophy |title=Becker muscular dystrophy &#124; Genetic and Rare Diseases Information Center (GARD) – an NCATS Program |format= |work= |accessdate=}}</ref>
* Becker's muscular [[dystrophy]] is caused by a [[mutation]] in the gene [[DMD]], one of the largest [[genes]] in humans.<ref name="pmid24305447">{{cite journal |vauthors=Wicklund MP |title=The muscular dystrophies |journal=Continuum (Minneap Minn) |volume=19 |issue=6 Muscle Disease |pages=1535–70 |date=December 2013 |pmid=24305447 |doi=10.1212/01.CON.0000440659.41675.8b |url=}}</ref> This [[gene]] encodes for the [[3685Y]] [[aminoacid]] protein called [[dystrophin]], wich can be found in [[Skeletal muscle|skeletal]] and [[Cardiac muscle cell|cardiac muscle]], among other tisues.<ref name="pmid24305447" />  This [[mutation]] produces a truncated [[dystrophin]] [[protein]] that will translate into a decreased but not incomplete functionality (difference from [[Duchenne muscular dystrophy|Duchenne]]).<ref name="IannacconeCastro2013">{{cite journal|last1=Iannaccone|first1=Susan T.|last2=Castro|first2=Diana|title=Congenital Muscular Dystrophies and Congenital Myopathies|journal=CONTINUUM: Lifelong Learning in Neurology|volume=19|year=2013|pages=1509–1534|issn=1080-2371|doi=10.1212/01.CON.0000440658.03557.f1}}</ref> <ref name="pmid203012986">{{cite journal |vauthors=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS |title= |journal= |volume= |issue= |pages= |date= |pmid=20301298 |doi= |url=}}</ref>
*Around 33% of patients with Becker's muscular dystrophy have [[de novo]] [[Mutation|mutations]].<ref name="pmid236206492" /> Point [[Mutation|mutations]] and [[duplications]] appear mostly from [[spermatogenesis]] while deletions arise from [[oogenesis]] in most of te cases.<ref name="pmid203012983">{{cite journal |vauthors=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS |title= |journal= |volume= |issue= |pages= |date= |pmid=20301298 |doi= |url=}}</ref> 
* On microscopic [[Histopathology|histopathological]] analysis, endomysial fibrosis with fatty replacement of [[muscle]] in later stages, [[inflammation]], increased internal [[nuclei]], [[Myofiber|myofibe]]<nowiki/>r cleavage with [[necrosis]], and [[phagocytosis]] are characteristic findings of Becker's muscular dystrophy.<ref name="SarkozyBushby20143" /><br />


== Pathophysiology[edit | edit source] ==
== Clinical Features ==
Unlike [[Duchenne muscular dystrophy]], Becker's muscular dystrophy (BMD) [[phenotype]] presents at a later age, widely variable onset from early [[childhood]] to late [[adulthood]], most of them falling in [[puberty]] range. Most of the patients will requiere a wheelchair after age 16.<ref name="pmid203012984">{{cite journal |vauthors=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS |title= |journal= |volume= |issue= |pages= |date= |pmid=20301298 |doi= |url=}}</ref>


* The pathogenesis of [disease name] is characterized by [feature1], [feature2], and [feature3].
Clinical presentation Becker's muscular [[dystrophy]] include:
* The [gene name] gene/Mutation in [gene name] has been associated with the development of [disease name], involving the [molecular pathway] pathway.
* On gross pathology, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].
* On microscopic histopathological analysis, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].


Becker's muscular dystrophy is caused by a mutation in the gene DMD, one of the largest genes in humans.<ref name="pmid243054476">{{cite journal| author=Wicklund MP| title=The muscular dystrophies. | journal=Continuum (Minneap Minn) | year= 2013 | volume= 19 | issue= 6 Muscle Disease | pages= 1535-70 | pmid=24305447 | doi=10.1212/01.CON.0000440659.41675.8b | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24305447  }}</ref> This gene encodes for the 3685Y aminoacid protein called dystrophin, wich can be found in skeletal and cardiac muscle, among other tisues. <ref name="pmid243054475">{{cite journal| author=Wicklund MP| title=The muscular dystrophies. | journal=Continuum (Minneap Minn) | year= 2013 | volume= 19 | issue= 6 Muscle Disease | pages= 1535-70 | pmid=24305447 | doi=10.1212/01.CON.0000440659.41675.8b | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24305447  }}</ref>
* Progressive symmetric muscle weakness, with a predilection in proximal muscles (eg. pelvic, legs, shoulders)<ref name="pmid203012984" />
*[[Congestive heart failure]]<ref name="SarkozyBushby20142" /><ref name="pmid203012988" /><ref name="pmid243054473">{{cite journal |vauthors=Wicklund MP |title=The muscular dystrophies |journal=Continuum (Minneap Minn) |volume=19 |issue=6 Muscle Disease |pages=1535–70 |date=December 2013 |pmid=24305447 |doi=10.1212/01.CON.0000440659.41675.8b |url=}}</ref>
*Calf [[hypertrophy]]<ref name="pmid203012984" /><ref name="pmid17162189" />
*[[Cramp|Cramping]] and [[muscle]] pain after exercise<ref name="SarkozyBushby20142">{{cite journal|last1=Sarkozy|first1=A.|last2=Bushby|first2=K.|last3=Mercuri|first3=E.|title=Muscular Dystrophies|year=2014|doi=10.1016/B978-0-12-801238-3.05597-5}}</ref><ref name="pmid17162189" />
* Flexion contractures<ref name="pmid203012984" /><ref name="pmid17162189" />
* Normal neck [[Flexion|flexor]] muscle [[Strength training|strength]] (differenting factor of BMD from [[Duchenne muscular dystrophy|DMD]])<ref name="pmid203012988">{{cite journal |vauthors=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS |title= |journal= |volume= |issue= |pages= |date= |pmid=20301298 |doi= |url=}}</ref>


There is an abcense of fasciculations, and this finding may exclude BMD<ref name="SarkozyBushby20142" /><ref name="pmid203012988" />


DMD and BMD are inherited in an X-linked recessive fashion, but in roughly 20% to 30% of cases, a mother does not test positive for the mutation in DMD. This is due to a high rate of new mutations, false maternity, and to germ-line mosaicism (in which the mutation is present in some tissues, such as ovaries, but not others, such as skeletal muscle). Because of the possibility of germ-line mosaicism, negative genetic testing in a mother does not preclude the possibility of an affected boy in a subsequent pregnancy. For this indication, preimplantation genetic testing is available.<ref name="pmid243054472">{{cite journal| author=Wicklund MP| title=The muscular dystrophies. | journal=Continuum (Minneap Minn) | year= 2013 | volume= 19 | issue= 6 Muscle Disease | pages= 1535-70 | pmid=24305447 | doi=10.1212/01.CON.0000440659.41675.8b | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24305447  }}</ref>
[[CNS]] is rarely afected in Becker's muscular [[dystrophy]], for this reason, [[Intelligence test|intelligence]] is usually spared.<ref name="pmid203012984" /><ref name="SarkozyBushby2014">{{cite journal|last1=Sarkozy|first1=A.|last2=Bushby|first2=K.|last3=Mercuri|first3=E.|title=Muscular Dystrophies|year=2014|doi=10.1016/B978-0-12-801238-3.05597-5}}</ref>


'''BMD.''' The BMD phenotype occurs when some dystrophin is produced, usually resulting from deletions or duplications that juxtapose in-frame exons, some splicing variants, and most non-truncating single-base changes that result in translation of a protein product with intact N and C termini. The shorter-than-normal dystrophin protein molecule, which retains partial function, produces the milder BMD phenotype.<ref name="pmid2030129810">{{cite journal| author=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K | display-authors=etal| title=GeneReviews® | journal= | year= 1993 | volume=  | issue=  | pages=  | pmid=20301298 | doi= | pmc= | url= }}</ref>
Most of women are [[asymptomatic]] [[carriers]], with very rare cases presenting the classic [[Symptom|symptoms]].<ref name="pmid203012984" /><ref name="pmid203012986" /><br />


== Clinical Features[edit | edit source] ==
== Differentiating Becker's muscular dystrophy from other Diseases ==
Duchenne muscular dystrophy (DMD) usually presents in early childhood with delayed motor milestones including delays in walking independently and standing up from a supine position. Proximal weakness causes a waddling gait and difficulty climbing stairs, running, jumping, and standing up from a squatting position. DMD is rapidly progressive, with affected children being wheelchair dependent by age 12 years. Cardiomyopathy occurs in almost all individuals with DMD after age 18 years. Few survive beyond the third decade, with respiratory complications and progressive cardiomyopathy being common causes of death.<ref name="pmid203012986">{{cite journal| author=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K | display-authors=etal| title=GeneReviews® | journal= | year= 1993 | volume=  | issue=  | pages=  | pmid=20301298 | doi= | pmc= | url= }}</ref>
Becker's muscular dystrophy must be differentiated from other diseases that cause skelletal and cardiac muscle afection, such as:


Becker muscular dystrophy (BMD) is characterized by later-onset skeletal muscle weakness. With improved diagnostic techniques, it has been recognized that the mild end of the spectrum includes men with onset of symptoms after age 30 years who remain ambulatory even into their 60s. Despite the milder skeletal muscle involvement, heart failure from DCM is a common cause of morbidity and the most common cause of death in BMD. Mean age of death is in the mid-40s.<ref name="pmid203012985">{{cite journal| author=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K | display-authors=etal| title=GeneReviews® | journal= | year= 1993 | volume= | issue= | pages= | pmid=20301298 | doi= | pmc= | url= }}</ref>
* [[Duchenne muscular dystrophy]]. Presents with most of the symptoms of Beckers muscular [[dystrophy]] but with an earlier and more severe onset, most of them having [[Symptom|symptoms]] from age 3 ([[Gowers' sign|Gower's sign]]); by convention, if a patient with a suspected [[dystrophinopathy]] stops walking before 12 years of age, he has DMD.<ref name="pmid243054473" /> Another diferentiating factor is the normal strength of neck flexor muscles in BMD.<ref name="pmid203012985">{{cite journal |vauthors=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS |title= |journal= |volume= |issue= |pages= |date= |pmid=20301298 |doi= |url=}}</ref>
* [[Limb-girdle muscular dystrophy|Limb-girdle muscular dystrophy (LGMD)]]. Is a group of [[inherited]] [[autosomal]] conditions that are clinically similar to [[dystrophynopathies]] (muscle [[Muscle weakness|weakness]] and [[wasting]]) but occur in both sexes. They are caused by a [[gene]] [[mutation]] that encodes [[sarcoglycans]].
* [[Emery-Dreifuss muscular dystrophy|Emery-Dreifuss muscular dystrophy (EDMD)]]. Is a [[Neuromuscular disease|neuromuscular]] disorder that may be inherited in an [[Autosomal chromosome|autosomal]] or [[X-linked]] mode. The classic clinical triad encompasses  incidious muscle [[Muscle weakness|weakness]] and [[wasting]] with predilection in the humero-peroneal distribution, joint [[Contracture|contractures]] in childhood, and cardiac afection that includes [[Palpitation|palpitations]], and syncope.<ref name="pmid17162189" />
* [[Spinal muscular atrophy|Spinal muscular atrophy(SMA)]]. Presents with muscle [[atrophy]], delayed [[weight]] and [[height]] gain, [[restrictive lung disease]], [[scoliosis]], [[Contractures|joint contractures]], and [[sleep]] difficulties. Is inherited in an [[autosomal recessive]] mode.<ref name="pmid203012985" /><ref name="pmid17162189" />
* [[Dilated cardiomyopathy|Dilated cardiomyopathy(DCM)]]. Familial variants may be inherited in an [[Autosomal chromosome|autosomal]] ([[Dominant gene|dominant]] or [[Recessive gene|recessive]]), or an [[X-linked]] fashion. Presents with symptoms of [[dyspnea]] and poor [[Exercise stress testing|exercise tolerance]].
* [[Barth syndrome]]. Is an X-linked disorder characterized by prepubertal [[growth delay]] followed by a growth spurt, muscle [[Muscle weakness|weakness]], [[Cardiomyopathy, Dilated|cardiomyopathy]], [[neutropenia]],  and [[facial gestalt]].<br />


CNS involvement is not common in MDs and intelligence is usually preserved.<ref name="SarkozyBushby2014">{{cite journal|last1=Sarkozy|first1=A.|last2=Bushby|first2=K.|last3=Mercuri|first3=E.|title=Muscular Dystrophies|year=2014|doi=10.1016/B978-0-12-801238-3.05597-5}}</ref>
== Screening ==
 
'''Becker muscular dystrophy (BMD)'''
 
* Progressive symmetric muscle weakness (proximal > distal) often with calf hypertrophy; weakness of quadriceps femoris in some cases the only sign
* Activity-induced cramping (present in some individuals)
* Flexion contractures of the elbows (if present, late in the course)
* Wheelchair dependency (after age 16 years); although some individuals remain ambulatory into their 30s and in rare cases into their 40s and beyond
* Preservation of neck flexor muscle strength (differentiates BMD from DMD)
 
Note: The presence of fasciculations or loss of sensory modalities excludes a suspected diagnosis of a dystrophinopathy. Individuals with an intermediate phenotype (outliers) have symptoms of intermediate severity and become wheelchair dependent between ages 13 and 16 years.<ref name="pmid203012987">{{cite journal| author=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K | display-authors=etal| title=GeneReviews® | journal= | year= 1993 | volume=  | issue=  | pages=  | pmid=20301298 | doi= | pmc= | url= }}</ref>


 
* [[Prenatal testing|Prenatal molecular genetic testing]] is recomended in couples planning to [[Pregnancy|conceive]] and have family members who are afected by or are [[Genetic carrier|carriers]] of a dystrophinopathy.<ref name="pmid2030129811">{{cite journal |vauthors=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS |title= |journal= |volume= |issue= |pages= |date= |pmid=20301298 |doi= |url=}}</ref>
Females may present with a classic dystrophinopathy or may be asymptomatic carriers.
* [[In utero|In-utero]] fetal [[muscle biopsy]] has also been realized under couples request for [[fetuses]] with a high [[probability]] of beign affected and inconclusive [[genetic linkage]].<ref name="pmid17041906">{{cite journal |vauthors=Deburgrave N, Daoud F, Llense S, Barbot JC, Récan D, Peccate C, Burghes AH, Béroud C, Garcia L, Kaplan JC, Chelly J, Leturcq F |title=Protein- and mRNA-based phenotype-genotype correlations in DMD/BMD with point mutations and molecular basis for BMD with nonsense and frameshift mutations in the DMD gene |journal=Hum. Mutat. |volume=28 |issue=2 |pages=183–95 |date=February 2007 |pmid=17041906 |doi=10.1002/humu.20422 |url=}}</ref>
 
* It is important to identify females at risk to be [[heterozygous]] of a [[dystrophinopathy]], in order to manage possible [[Cardiomyopathies|cardiac]] complications; this can be done by [[Genetic testing|molecular genetic testing]], [[CK]] measurements, and [[Genetic linkage|linkage]] analysis.<ref name="pmid17041906" /><ref name="pmid2030129811" />
* '''Females with a classic dystrophinopathy.''' The genetic mechanisms that can explain this rare occurrence (and testing to identify the cause) include the following:
** A deletion involving Xp21.2 (microarray [CMA] studies)
** An X-chromosome rearrangement involving Xp21.2 or complete absence of an X chromosome (i.e., Turner syndrome) (cytogenetic studies)
** Uniparental disomy (UPD) of the X chromosome (UPD studies)
** Compound heterozygosity for two ''DMD'' pathogenic variants [Soltanzadeh et al 2010] (deletion/duplication analysis and/or sequence analysis)
** Nonrandom X-chromosome inactivation (XCI). See Genotype-Phenotype Correlations.<ref name="pmid203012989">{{cite journal| author=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K | display-authors=etal| title=GeneReviews® | journal= | year= 1993 | volume= | issue= | pages= | pmid=20301298 | doi= | pmc= | url= }}</ref>


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== Differentiating [disease name] from other Diseases[edit | edit source] ==
== Epidemiology and Demographics ==
 
* [Disease name] must be differentiated from other diseases that cause [clinical feature 1], [clinical feature 2], and [clinical feature 3], such as:
 
'''Limb-girdle muscular dystrophy''' '''(LGMD)''' is a group of autosomal recessive and autosomal dominant disorders that are clinically similar to DMD but occur in both sexes. Limb-girdle dystrophies are caused by mutation of genes that encode sarcoglycans and other proteins associated with the muscle cell membrane that interact with dystrophin [Mohassel & Bönnemann 2015]. Testing for deficiency of proteins from the transmembrane sarcoglycan complex and of other proteins is indicated in individuals with dystrophin-positive dystrophies. LGMD type 2I phenotypically resembles DMD and BMD and is caused by biallelic pathogenic variants in ''FKRP'' (encoding fukutin-related protein).<ref name="pmid20301298">{{cite journal| author=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K | display-authors=etal| title=GeneReviews® | journal= | year= 1993 | volume=  | issue=  | pages=  | pmid=20301298 | doi= | pmc= | url= }}</ref>


'''Emery-Dreifuss muscular dystrophy''' '''(EDMD)''' is characterized by the clinical triad of joint contractures that begin in early childhood, slowly progressive muscle weakness and wasting initially in a humero-peroneal distribution that later extends to the scapular and pelvic girdle muscles, and cardiac involvement that may include palpitations, presyncope and syncope, poor exercise tolerance, and congestive heart failure. Age of onset, severity, and progression of the muscle and cardiac involvement show intra- and interfamilial variation. Clinical variability ranges from early and severe presentation in childhood to a late onset and slowly progressive course. In general, joint contractures appear during the first two decades, followed by muscle weakness and wasting. Cardiac involvement usually occurs after the second decade. Pathogenic variants in three genes are known to cause EDMD: ''EMD'' and ''FHL1'', which cause X-linked EDMD; and ''LMNA'', which causes autosomal dominant EDMD and autosomal recessive EDMD.<ref name="pmid203012982">{{cite journal| author=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K | display-authors=etal| title=GeneReviews® | journal= | year= 1993 | volume=  | issue=  | pages=  | pmid=20301298 | doi= | pmc= | url= }}</ref>
* The [[prevalence]] of Becker's muscular dystrophy is approximately 1-3 per 100,000 individuals.
* The [[incidence]] of Becker's muscular dystrophy is approximately 3-6 per 100,000 male [[births]] worldwide.


'''Spinal muscular atrophy''' '''(SMA)''' is suspected in individuals with poor muscle tone, muscle weakness that spares the face and ocular muscles, and evidence of anterior horn cell involvement, including fasciculations of the tongue and absence of deep tendon reflexes. The onset of weakness ranges from before birth to adolescence or young adulthood. The weakness is symmetric, proximal > distal, and progressive. Poor weight gain with growth failure, restrictive lung disease, scoliosis, joint contractures, and sleep difficulties are common complications. SMA is caused by pathogenic variants in ''SMN1'' and inherited in an autosomal recessive manner.
=== Age ===
Becker's muscular dystrophy is diagnosed in 85% of patients by age 25.<ref name="pmid1673177">{{cite journal |vauthors=Bushby KM, Thambyayah M, Gardner-Medwin D |title=Prevalence and incidence of Becker muscular dystrophy |journal=Lancet |volume=337 |issue=8748 |pages=1022–4 |date=April 1991 |pmid=1673177 |doi=10.1016/0140-6736(91)92671-n |url=}}</ref>


'''Dilated cardiomyopathy''' '''(DCM)''' can be familial or nonfamilial. In a large series in which family studies were performed, one third to one half of individuals had nonfamilial DCM and two thirds had familial DCM. Familial DCM may be inherited in an autosomal dominant, an autosomal recessive, or an X-linked manner. Most familial DCM (probably 80%-90%) appears to be autosomal dominant; X-linked and autosomal recessive forms are less common [Watkins et al 2011].<ref name="pmid203012983">{{cite journal| author=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K | display-authors=etal| title=GeneReviews® | journal= | year= 1993 | volume= | issue=  | pages=  | pmid=20301298 | doi= | pmc= | url= }}</ref>
=== Gender ===
 
Becker's muscular dystrophy affects mostly men, women are [[Genetic carrier|carriers]] almost exclusively (except rare situation).<ref name="pmid2030129813">{{cite journal |vauthors=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS |title= |journal= |volume= |issue= |pages= |date= |pmid=20301298 |doi= |url=}}</ref>
'''Barth syndrome,''' an X-linked disorder caused by mutation of ''TAZ'', is characterized in affected males by cardiomyopathy, neutropenia, skeletal myopathy, prepubertal growth delay, and distinctive facial gestalt (most evident in infancy); not all features may be present in a given affected individual. Cardiomyopathy, which is almost always present before age five years, is typically dilated cardiomyopathy with or without endocardial fibroelastosis or left ventricular non-compaction. Heart failure is a significant cause of morbidity and mortality; risk of arrhythmia and sudden death is increased. The non-progressive myopathy predominantly affects the proximal muscles, and results in early motor delays. Prepubertal growth delay is followed by a postpubertal growth spurt with remarkable "catch-up" growth.<ref name="pmid203012984">{{cite journal| author=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K | display-authors=etal| title=GeneReviews® | journal= | year= 1993 | volume= | issue= | pages= | pmid=20301298 | doi= | pmc= | url= }}</ref>
<br />
 
== Screening ==
It is appropriate to evaluate at-risk female family members (i.e., the sisters or maternal female relatives of an affected male and first-degree relatives of a known or possible heterozygous female) in order to identify as early as possible heterozygous females who would benefit from cardiac surveillance (see Surveillance).


Evaluations can include the following:
=== Race ===


* Molecular genetic testing if the ''DMD'' pathogenic variant in the family is known
* Becker's muscular dystrophy usually affects individuals of the hispanic race.<ref name="urlPrevalence of Duchenne / Becker Muscular Dystrophies | CDC">{{cite web |url=https://www.cdc.gov/ncbddd/musculardystrophy/features/key-findings-population-duchenne.html |title=Prevalence of Duchenne / Becker Muscular Dystrophies &#124; CDC |format= |work= |accessdate=}}</ref><ref name="pmid198344522">{{cite journal |vauthors= |title=Prevalence of Duchenne/Becker muscular dystrophy among males aged 5-24 years - four states, 2007 |journal=MMWR Morb. Mortal. Wkly. Rep. |volume=58 |issue=40 |pages=1119–22 |date=October 2009 |pmid=19834452 |doi= |url=}}</ref>
* Serum CK testing if the pathogenic variant in the family is not known. Although serum CK concentration can be normal in carrier females, if elevated, it will support heterozygosity status in a female relative.
* Asian individuals are less likely to develop Becker's muscular dystrophy.<ref name="urlPrevalence of Duchenne / Becker Muscular Dystrophies | CDC" /><ref name="pmid198344522" />
* Molecular genetic testing of the at-risk female if an affected male is not available for testing:
** By deletion/duplication analysis first
** If no pathogenic variant is identified, by sequence analysis
* Linkage analysis to determine carrier status in at-risk females if (1) the ''DMD'' pathogenic variant in the proband is not known, (2) no ''DMD'' pathogenic variant or serum CK elevation is identified in a carrier female, and (3) the family has more than one affected male with the unequivocal diagnosis of DMD/BMD/''DMD''-associated DCM
** Linkage studies are based on accurate clinical diagnosis of DMD/BMD/''DMD''-associated DCM in the affected family members and accurate understanding of the genetic relationships in the family.
** Linkage analysis relies on the availability and willingness of family members to be tested.
** Because the markers used for linkage in DMD/BMD/''DMD''-associated DCM are highly informative and lie both within and flanking the ''DMD'' locus, they can be used in most families with DMD/BMD/''DMD''-associated DCM [Kim et al 2002]. Note: (1) The large size of ''DMD'' leads to an appreciable risk of recombination. It has been estimated that the gene itself spans a genetic distance of 12 centimorgans [Abbs et al 1990]; thus, multiple recombination events among different members of a family may complicate the interpretation of a linkage study. (2)Testing by linkage analysis is not possible for families in which there is a single affected male. (3) Testing by linkage analysis may not be widely available on a clinical basis.


See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.<ref name="pmid170419065">{{cite journal| author=Deburgrave N, Daoud F, Llense S, Barbot JC, Récan D, Peccate C | display-authors=etal| title=Protein- and mRNA-based phenotype-genotype correlations in DMD/BMD with point mutations and molecular basis for BMD with nonsense and frameshift mutations in the DMD gene. | journal=Hum Mutat | year= 2007 | volume= 28 | issue= 2 | pages= 183-95 | pmid=17041906 | doi=10.1002/humu.20422 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17041906  }}</ref>
== Risk Factors ==
<br />


=== Prenatal Testing and Preimplantation Genetic Diagnosis ===
* Becker's muscular dystrophy is developed in the majority of cases from males who are born from [[genetic carrier]] mothers or by [[Mutation|spontaneous mutation]], there has not been any [[Risk factor|risk factors]] implicated for a [[DMD]] gene mutation.<ref name="pmid198344523">{{cite journal |vauthors= |title=Prevalence of Duchenne/Becker muscular dystrophy among males aged 5-24 years - four states, 2007 |journal=MMWR Morb. Mortal. Wkly. Rep. |volume=58 |issue=40 |pages=1119–22 |date=October 2009 |pmid=19834452 |doi= |url=}}</ref>
'''Molecular genetic testing.''' Once the ''DMD'' pathogenic variant has been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic diagnosis for a dystrophinopathy are possible.
* Studies have found that several [[Genetics|genetic]] [[polymorphisms]] and [[Mutation|mutations]] may be a factor for Becker's muscular dystrophy progression, but further [[research]] is necessary to draw conclusions.<ref name="pmid27018093">{{cite journal |vauthors=Barakat-Haddad C, Shin S, Candundo H, Lieshout PV, Martino R |title=A systematic review of risk factors associated with muscular dystrophies |journal=Neurotoxicology |volume=61 |issue= |pages=55–62 |date=July 2017 |pmid=27018093 |doi=10.1016/j.neuro.2016.03.007 |url=}}</ref> <br />
== Natural History, Complications and Prognosis ==


'''Fetal muscle biopsy.''' In utero fetal muscle biopsy has been used in the prenatal diagnosis of DMD in families with DMD in which the ''DMD'' pathogenic variant is not known [Ladwig et al 2002].
* The majority of patients with Becker's muscular [[dystrophy]] remain [[asymptomatic]] until [[adolescence]].<ref name="pmid975594">{{cite journal |vauthors=Emery AE, Skinner R |title=Clinical studies in benign (Becker type) X-linked muscular dystrophy |journal=Clin. Genet. |volume=10 |issue=4 |pages=189–201 |date=October 1976 |pmid=975594 |doi=10.1111/j.1399-0004.1976.tb00033.x |url=}}</ref>
* Early clinical features include calf hypertrophy, difficulty rising from a chair, [[Anatomical terms of location|proximal]] muscle [[Muscle weakness|weakness]], climbing stairs, sustaining [[Imbalance|balance]], elevating arms, and in later stages [[heart failure]].<ref name="pmid203012989" /><ref name="pmid23097603">{{cite journal |vauthors=Passamano L, Taglia A, Palladino A, Viggiano E, D'Ambrosio P, Scutifero M, Rosaria Cecio M, Torre V, DE Luca F, Picillo E, Paciello O, Piluso G, Nigro G, Politano L |title=Improvement of survival in Duchenne Muscular Dystrophy: retrospective analysis of 835 patients |journal=Acta Myol |volume=31 |issue=2 |pages=121–5 |date=October 2012 |pmid=23097603 |pmc=3476854 |doi= |url=}}</ref>
* The most common complications in Becker's muscular dystrophy are [[Cardiac failure|cardiac]] and [[Respiratory failure|respiratory]] failure, [[Pneumonia|pneumonias]], and in rare cases [[cognitive impairment]].<ref name="pmid975594" /><ref name="urlwww.mda.org">{{cite web |url=https://www.mda.org/sites/default/files/publications/Facts_DMD-BMD_P-211_0.pdf |title=www.mda.org |format= |work= |accessdate=}}</ref>
* [[Prognosis]] is generally poor, depending on [[spectrum]] of Becker's muscular dystrophy, but much better that [[Duchenne muscular dystrophy]]. In 2002, the [[Survival analysis|survival]] rate at age 20 was 60%.<ref name="pmid17162189" /><ref name="urlPathology Outlines - Becker muscular dystrophy">{{cite web |url=https://www.pathologyoutlines.com/topic/musclebeckermusculardystrophy.html |title=Pathology Outlines - Becker muscular dystrophy |format= |work= |accessdate=}}</ref>
* If left [[untreated]], the majority of patients with Becker's muscular dystrophy may die due to [[Cardiac failure|cardiac]] and [[Respiratory failure|respiratory]] failure in their mid-40's.<ref name="pmid203012989">{{cite journal |vauthors=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS |title= |journal= |volume= |issue= |pages= |date= |pmid=20301298 |doi= |url=}}</ref>
* Cradiac, respiratory, and orthopedic care has greatly improved in last years for patients with Becker disease, this, increasing the life span in these individuals.<ref name="pmid2030129814">{{cite journal |vauthors=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS |title= |journal= |volume= |issue= |pages= |date= |pmid=20301298 |doi= |url=}}</ref>


The history of molecular diagnostic testing in DMD and the impact of new techniques including chromosome microarray (CMA) analysis and noninvasive prenatal diagnosis methods are reviewed in various publications [Raymond et al 2010, Xu et al 2015, Parks et al 2016].<ref name="pmid170419066">{{cite journal| author=Deburgrave N, Daoud F, Llense S, Barbot JC, Récan D, Peccate C | display-authors=etal| title=Protein- and mRNA-based phenotype-genotype correlations in DMD/BMD with point mutations and molecular basis for BMD with nonsense and frameshift mutations in the DMD gene. | journal=Hum Mutat | year= 2007 | volume= 28 | issue= 2 | pages= 183-95 | pmid=17041906 | doi=10.1002/humu.20422 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17041906  }}</ref>
<br />
<br />


== Epidemiology and Demographics[edit | edit source] ==
== Diagnosis ==
 
The diagnosis of Becker's muscular dystrophy is made with a classic clinical presentation plus elevated [[Creatine kinase|CK]], [[Molecular genetic analysis|molecular genetic testing]], or [[muscle biopsy]].<ref name="pmid2030129816" />
* The prevalence of Becker's muscular dystrophy is approximately 3-6 per 100,000 individuals worldwide.
* In [year], the incidence of [disease name] was estimated to be [number or range] cases per 100,000 individuals in [location].
 
=== Age[edit | edit source] ===
 
* Patients of all age groups may develop [disease name].
 
* [Disease name] is more commonly observed among patients aged [age range] years old.
* [Disease name] is more commonly observed among [elderly patients/young patients/children].
 
=== Gender[edit | edit source] ===
Becker's muscular dystrophy affects men almost exclusively.
 
* [Gender 1] are more commonly affected with [disease name] than [gender 2].
* The [gender 1] to [Gender 2] ratio is approximately [number > 1] to 1.


=== Race[edit | edit source] ===
=== Symptoms ===
Symptoms of Becker's muscular dystrophy may include the following:


* There is no racial predilection for [disease name].
* [[Anatomical terms of location|Proximal]] [[muscle weakness]]<ref name="urlwww.mda.org" /><ref name="pmid23097603" />
* [[Myalgia|Myalgias]]<ref name="urlwww.mda.org" /><ref name="pmid2030129816" />
* [[Cramp|Muscle cramps]]<ref name="urlwww.mda.org" />
* [[Imbalance]]<ref name="urlwww.mda.org" /><ref name="pmid2030129816">{{cite journal |vauthors=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS |title= |journal= |volume= |issue= |pages= |date= |pmid=20301298 |doi= |url=}}</ref>
* [[Toe walking]]<ref name="pmid23097603" />
* Difficulty raising from a chair<ref name="urlwww.mda.org" /><ref name="pmid23097603" /><ref name="pmid2030129816" />
* Difficulty [[climbing]] stairs<ref name="urlwww.mda.org" /><ref name="pmid2030129816" />
* Difficulty raising the arms<ref name="urlwww.mda.org" /><ref name="pmid23097603" />
* [[Cardiac failure|Heart failure]]<ref name="urlwww.mda.org" />
* [[Dyspnea]]<ref name="pmid2030129816" />


* [Disease name] usually affects individuals of the [race 1] race.
=== Physical Examination ===
* [Race 2] individuals are less likely to develop [disease name].
Patients with Becker's muscular dystrophy usually adopt a posture with shoulders held back, abdomen stuck out, and lumbar hyperlordosis.<ref name="pmid2760082" />


== Risk Factors[edit | edit source] ==
Physical examination may be remarkable for:


* Common risk factors in the development of [disease name] are [risk factor 1], [risk factor 2], [risk factor 3], and [risk factor 4].
*Calf [[Hypertrophy (medical)|hypertrophy]]<ref name="urlwww.mda.org" />
*[[Gowers sign]]<ref name="urlwww.mda.org" />
*[[Cardiac arrhythmia|Arrythmias]]<ref name="urlwww.mda.org" />


== Natural History, Complications and Prognosis[edit | edit source] ==
=== Laboratory Findings ===
An elevated [[Creatine kinase|CK]] is typical in Becker's muscular [[dystrophy]], with a peak around 10-15 years of age.<ref name="pmid243054472" />


* The majority of patients with [disease name] remain asymptomatic for [duration/years].
Other laboratory findings consistent with Becker's muscular dystrophy may be:
* Early clinical features include [manifestation 1], [manifestation 2], and [manifestation 3].
* If left untreated, [#%] of patients with [disease name] may progress to develop [manifestation 1], [manifestation 2], and [manifestation 3].
* Common complications of [disease name] include [complication 1], [complication 2], and [complication 3].
* Prognosis is generally [excellent/good/poor], and the [1/5/10­year mortality/survival rate] of patients with [disease name] is approximately [#%].


In the early stages, Duchenne and Becker MD affect the shoulder and upper arm muscles and the muscles of the hips and thighs. These weaknesses lead to difficulty in rising from the floor, climbing stairs, maintaining balance and raising the arms.
* Elevated [[Alanine transaminase|ALT]]/[[ASTL|AST]]<ref name="pmid243054472">{{cite journal |vauthors=Wicklund MP |title=The muscular dystrophies |journal=Continuum (Minneap Minn) |volume=19 |issue=6 Muscle Disease |pages=1535–70 |date=December 2013 |pmid=24305447 |doi=10.1212/01.CON.0000440659.41675.8b |url=}}</ref>
* [[Myoglobinuria]] when strenous [[Physical exercise|physical activity]]<ref name="pmid170419062">{{cite journal |vauthors=Deburgrave N, Daoud F, Llense S, Barbot JC, Récan D, Peccate C, Burghes AH, Béroud C, Garcia L, Kaplan JC, Chelly J, Leturcq F |title=Protein- and mRNA-based phenotype-genotype correlations in DMD/BMD with point mutations and molecular basis for BMD with nonsense and frameshift mutations in the DMD gene |journal=Hum. Mutat. |volume=28 |issue=2 |pages=183–95 |date=February 2007 |pmid=17041906 |doi=10.1002/humu.20422 |url=}}</ref>
* Normal [[Gamma-glutamyl transpeptidase|GGT]]<ref name="pmid26022459">{{cite journal |vauthors=Lee SH, Lee JH, Lee KA, Choi YC |title=Clinical and Genetic Characterization of Female Dystrophinopathy |journal=J Clin Neurol |volume=11 |issue=3 |pages=248–51 |date=July 2015 |pmid=26022459 |pmc=4507379 |doi=10.3988/jcn.2015.11.3.248 |url=}}</ref>


== Diagnosis[edit | edit source] ==
=== Hystopathology ===
[[Histological section|Histologic]] findings in Becker's muscular may be:


=== Diagnostic Criteria[edit | edit source] ===
* [[Atrophy|Atrophic]] small [[myofibers]]<ref name="SarkozyBushby20143" />
* [[Skeletal muscle|Muscle fibers]] [[necrosis]] and regeneration<ref name="SarkozyBushby20143" /><ref name="urlPathology Outlines - Becker muscular dystrophy" />
* [[Endomysium|Endomysial]] [[fibrosis]] and fatty replacement of [[muscle]]<ref name="SarkozyBushby20143" />
* [[Inflammation]]<ref name="SarkozyBushby20143" /><ref name="urlPathology Outlines - Becker muscular dystrophy" />


* The diagnosis of [disease name] is made when at least [number] of the following [number] diagnostic criteria are met:
=== EMG ===
[[Electromyography|EMG]] in Becker's muscular [[dystrophy]], may reveal myopathic [[motor units]] with or without [[muscle membrane]] instability.<ref name="pmid243054472" /><ref name="pmid30356714">{{cite journal |vauthors=Naddaf E, Milone M, Mauermann ML, Mandrekar J, Litchy WJ |title=Muscle Biopsy and Electromyography Correlation |journal=Front Neurol |volume=9 |issue= |pages=839 |date=2018 |pmid=30356714 |pmc=6189315 |doi=10.3389/fneur.2018.00839 |url=}}</ref>


:* [criterion 1]
=== Echocardiography ===
:* [criterion 2]
[[Echocardiography|Echocardiogram]] should be done at the time of diagnosis.<ref name="pmid30356714" /><ref name="pmid2030129817">{{cite journal |vauthors=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS |title= |journal= |volume= |issue= |pages= |date= |pmid=20301298 |doi= |url=}}</ref>
:* [criterion 3]
:* [criterion 4]
 
=== Symptoms[edit | edit source] ===
 
* [Disease name] is usually asymptomatic.
* Symptoms of [disease name] may include the following:
 
:* [symptom 1]
:* [symptom 2]
:* [symptom 3]
:* [symptom 4]
:* [symptom 5]
:* [symptom 6]
 
=== Physical Examination[edit | edit source] ===
 
* Patients with [disease name] usually appear [general appearance].
* Physical examination may be remarkable for:
 
:* [finding 1]
:* [finding 2]
:* [finding 3]
:* [finding 4]
:* [finding 5]
:* [finding 6]
 
=== Laboratory Findings[edit | edit source] ===
 
* There are no specific laboratory findings associated with [disease name].
 
* A [positive/negative] [test name] is diagnostic of [disease name].
* An [elevated/reduced] concentration of [serum/blood/urinary/CSF/other] [lab test] is diagnostic of [disease name].
* Other laboratory findings consistent with the diagnosis of [disease name] include [abnormal test 1], [abnormal test 2], and [abnormal test 3].
 
=== Imaging Findings[edit | edit source] ===
 
* There are no [imaging study] findings associated with [disease name].
 
* [Imaging study 1] is the imaging modality of choice for [disease name].
* On [imaging study 1], [disease name] is characterized by [finding 1], [finding 2], and [finding 3].
* [Imaging study 2] may demonstrate [finding 1], [finding 2], and [finding 3].
 
=== Other Diagnostic Studies[edit | edit source] ===
 
* [Disease name] may also be diagnosed using [diagnostic study name].
* Findings on [diagnostic study name] include [finding 1], [finding 2], and [finding 3].
 
The diagnosis of a dystrophinopathy is established in a proband with the characteristic clinical findings and elevated CK concentration and/or by identification of a hemizygous pathogenic variant in ''DMD'' on molecular genetic testing in a male and of a heterozygous pathogenic variant in ''DMD'' on molecular genetic testing in a female. Females may present with a classic dystrophinopathy or may be asymptomatic carriers.<ref name="pmid203012988">{{cite journal| author=Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH, Stephens K | display-authors=etal| title=GeneReviews® | journal= | year= 1993 | volume=  | issue=  | pages=  | pmid=20301298 | doi= | pmc= | url= }}</ref>
 
 
A dystrophinopathy should be suspected in any male or female patient presenting with progressive limb-girdle weakness, especially if the patient has a positive family history, substantially elevated CK level, or cardiomyopathy. The diagnosis of DMD should be the physician’s first thought when a 3- to 5- year-old boy who is physically slower than his peers presents with toe walking, large calves, neck weakness, a partial Gower’s sign, and a CK level greater than 3000 U/L. CK levels may be elevated 10- to 200-fold. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT), which are also muscle enzymes, are often elevated. This transaminitis reflects muscle involvement rather than liver disease, and this can be verified by checking the liver-specific transaminase +-glutamyltransferase (GGT), which will be normal. In DMD, DNA analysis of the dystrophin gene is the first diagnostic procedure.<ref name="pmid243054473">{{cite journal| author=Wicklund MP| title=The muscular dystrophies. | journal=Continuum (Minneap Minn) | year= 2013 | volume= 19 | issue= 6 Muscle Disease | pages= 1535-70 | pmid=24305447 | doi=10.1212/01.CON.0000440659.41675.8b | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24305447  }}</ref>
 
In patients with BMD or in manifesting female carriers, weakness may not be as pronounced, the CK level may be lower, and the initial procedure will often be electrodiagnostic testing. The EMG reveals myopathic motor units with or without muscle membrane instability. If the patient has no family history of a dystrophinopathy, then a muscle biopsy may be performed. Immunostaining for the N-terminal, rod, and C-terminal regions of dystrophin will usually reveal diffusely decreased, or patchy, staining of some but not all muscle fiber membranes. Confirmatory testing is through DNA analysis. Mutation analysis consists of analysis for duplications and deletions via multiplex PCR or multiplex ligationdependent probe amplification. If this is negative, then gene sequencing is undertaken. Mutations in DMD causative for DMD and BMD are fairly consistent when assessed across different countries,13Y16 with the composition including 43% to 67% deletions and 9% to 11% duplications of exons, 16% to 26% point mutations, and 5% to 6% splice site mutations. Therapies allowing multiexon skipping from exons 45 through 55 would benefit more than 50% of patients with DMD. Mutations disrupting the reading frame (out-of-frame mutations) in DMD create a truncated RNA transcript that is rapidly degraded. This leads to a virtual absence of dystrophin in muscle and a DMD phenotype. Mutations with maintenance of the reading frame (in-frame mutations) generate shorter or less stable dystrophin. Dystrophin with in-frame mutations retain their amino- and carboxy-terminus domains and thus still maintain the mechanical bridge between actin and "-dystroglycan. Inframe mutations more often lead to a BMD phenotype. In a large series, out-of-frame mutations led to a DMD phenotype in nearly 90% of cases; however, in-frame mutations led to a BMD phenotype in only approximately 60% of cases (Case 2-1).13 <ref name="pmid243054474">{{cite journal| author=Wicklund MP| title=The muscular dystrophies. | journal=Continuum (Minneap Minn) | year= 2013 | volume= 19 | issue= 6 Muscle Disease | pages= 1535-70 | pmid=24305447 | doi=10.1212/01.CON.0000440659.41675.8b | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24305447  }}</ref>
 
== Treatment[edit | edit source] ==
 
=== Medical Therapy[edit | edit source] ===
 
* There is no treatment for [disease name]; the mainstay of therapy is supportive care.
 
* The mainstay of therapy for [disease name] is [medical therapy 1] and [medical therapy 2].
* [Medical therapy 1] acts by [mechanism of action 1].
* Response to [medical therapy 1] can be monitored with [test/physical finding/imaging] every [frequency/duration].
 
*
*
 
Physical therapy to promote mobility and prevent contractures
 
* Exercise
** All ambulatory boys with DMD or those in early non-ambulatory phase should participate in regular gentle exercise to avoid contractures and disuse atrophy.
** Exercise can consist of a combination of swimming pool and recreation-based activities. Swimming can be continued in non-ambulatory patients under close supervision, if medically safe.
** If patients complain of muscle pain during or after exercise, the activity should be reduced and monitoring for myoglobinuria should be carried out. Myoglobinuria within 24 hours after exercise indicates overexertion leading to rhabdomyolysis.<ref name="pmid170419064">{{cite journal| author=Deburgrave N, Daoud F, Llense S, Barbot JC, Récan D, Peccate C | display-authors=etal| title=Protein- and mRNA-based phenotype-genotype correlations in DMD/BMD with point mutations and molecular basis for BMD with nonsense and frameshift mutations in the DMD gene. | journal=Hum Mutat | year= 2007 | volume= 28 | issue= 2 | pages= 183-95 | pmid=17041906 | doi=10.1002/humu.20422 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17041906  }}</ref>


=== Imaging Findings ===
There are no [[X-ray]] findings characteristic with  with Becker's muscular dystrophy, but [[scoliosis]] may be found.<ref name="pmid2760082">{{cite journal |vauthors=Smith AD, Koreska J, Moseley CF |title=Progression of scoliosis in Duchenne muscular dystrophy |journal=J Bone Joint Surg Am |volume=71 |issue=7 |pages=1066–74 |date=August 1989 |pmid=2760082 |doi= |url=}}</ref>   
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== Treatment ==


=== Surgery[edit | edit source] ===
=== Medical Therapy ===
 
* Surgery is the mainstay of therapy for [disease name].
* [Surgical procedure] in conjunction with [chemotherapy/radiation] is the most common approach to the treatment of [disease name].
* [Surgical procedure] can only be performed for patients with [disease stage] [disease name].
 
=== Prevention[edit | edit source] ===
 
* There are no primary preventive measures available for [disease name].
 
* Effective measures for the primary prevention of [disease name] include [measure1], [measure2], and [measure3].
 
* Once diagnosed and successfully treated, patients with [disease name] are followed-up every [duration]. Follow-up testing includes [test 1], [test 2], and [test 3].
 
Appropriate management of individuals with a dystrophinopathy can prolong survival and improve quality of life.<ref name="pmid170419062">{{cite journal| author=Deburgrave N, Daoud F, Llense S, Barbot JC, Récan D, Peccate C | display-authors=etal| title=Protein- and mRNA-based phenotype-genotype correlations in DMD/BMD with point mutations and molecular basis for BMD with nonsense and frameshift mutations in the DMD gene. | journal=Hum Mutat | year= 2007 | volume= 28 | issue= 2 | pages= 183-95 | pmid=17041906 | doi=10.1002/humu.20422 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17041906  }}</ref>
 
 
''Prevention of secondary complications:'' Evaluation by a pulmonologist and cardiologist before surgeries; pneumococcal and influenza immunizations annually; nutrition assessment; physical therapy to promote mobility and prevent contractures; sunshine and a balanced diet rich in vitamin D and calcium to improve bone density and reduce the risk of fractures; weight control to avoid obesity.<ref name="pmid170419067">{{cite journal| author=Deburgrave N, Daoud F, Llense S, Barbot JC, Récan D, Peccate C | display-authors=etal| title=Protein- and mRNA-based phenotype-genotype correlations in DMD/BMD with point mutations and molecular basis for BMD with nonsense and frameshift mutations in the DMD gene. | journal=Hum Mutat | year= 2007 | volume= 28 | issue= 2 | pages= 183-95 | pmid=17041906 | doi=10.1002/humu.20422 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17041906  }}</ref>


* There is no definitive treatment for Becker's muscular [[dystrophy]]; treatment will be [[Multidisciplinary care|multidisciplinary]] depending on [[Comorbidity|comorbidities]]; the mainstay of therapy is [[supportive care]].<ref name="SarkozyBushby20144" />
* [[Corticosteroid medications|Corticosteroids]] have shown to improve strength in other [[dystrophinopathies]], but its efficacy on Beckers muscular dystrophy is uncertain. To measure improvement with [[corticosteroid]] therapy, [[timed muscle function tests]], [[pulmonary function tests]], and age at loss of [[independent ambulation]] are registered.<ref name="pmid2030129817" />
* The management of [[Scoliosis (patient information)|scoliosis]] is bracing and [[surgery]] in some cases.<ref name="urlPathology Outlines - Becker muscular dystrophy" />
* [[Beta-blockers]], [[ARBs|angiotensin II-receptor blockers]], and [[ACE inhibitor|ACE inhibitors]] are used to improve [[ventricular function]] in patients with Becker's muscular [[dystrophy]] when [[Ejection fraction|EF]] is less than 55%.<ref name="SarkozyBushby20144">{{cite journal|last1=Sarkozy|first1=A.|last2=Bushby|first2=K.|last3=Mercuri|first3=E.|title=Muscular Dystrophies|year=2014|doi=10.1016/B978-0-12-801238-3.05597-5}}</ref>
* [[Physical exercise|Low impact exercise]] (eg. [[swimming]]) should be advised. If [[myalgia]] presents, [[Physical exercise|physical activity]] should be reduced and [[myoglobinuria]] cheked out.<ref name="pmid2030129817" />


'''Cardiomyopathy.''' Recommendations are based on an American Academy of Pediatrics policy statement and various additional publications [American Academy of Pediatrics Section on Cardiology and Cardiac Surgery 2005, Jefferies et al 2005, Viollet et al 2012] and apply to patients with the DMD or BMD phenotype.
=== Surgery ===


* The authors' institution commonly treats children with DMD or BMD early with an ACE inhibitor and/or beta blocker.
* [[Heart transplantation|Cardiac transplantation]] may be requiered in patients with severe [[Dilated cardiomyopathy classification|dilated cardiomyopathy]].<ref name="pmid2030129817" />
* When used in combination, these appear to lead to initial improvement of left ventricular function; however, ACE inhibitors are also used without beta blockers, with similar results [Viollet et al 2012].
* The optimal time to start treatment in DMD is unknown, but most cardiologists will initiate treatment when the left ventricle ejection fraction drops below 55% and fractional shortening is less than 28% [Jefferies et al 2005, Viollet et al 2012].
* Angiotensin II-receptor blockers (ARBs) such as losartan are similarly effective and can be used in cases of poor tolerability of ACE inhibitors [Allen et al 2013].
* In cases of overt heart failure, other heart failure therapies including diuretics and digoxin are used as needed.
* Cardiac transplantation is offered to persons with severe dilated cardiomyopathy and BMD with limited or no clinical evidence of skeletal muscle disease.


'''Scoliosis''' treatment as needed is appropriate. The management of scoliosis involves bracing and surgery. Most patients end up getting a spinal fusion. The use of rods is not contraindicated; therefore, rod and bone grafts are used to fuse the spine. A minority of patients do not develop significant scoliosis and may not require a spinal fusion.
* Severe or incapacitating [[scoliosis]] may be corrected with [[surgery]].<ref name="pmid2030129817" />


'''Corticosteroid therapy.''' Studies have shown that corticosteroids improve the muscle strength and function of individuals with DMD (see Corticosteroid Therapy in DMD). This therapy remains the treatment of choice for affected individuals between ages five and 15 years. Corticosteroid therapy is not recommended in children before age two years [Bushby et al 2010a]. This treatment is also used in BMD, although the efficacy is less clear (see '''BMD''' below).
=== Primary Prevention ===
There are no primary preventive measures available for Becker's muscular [[dystrophy]].<ref name="urlPathology Outlines - Becker muscular dystrophy" />


The following published recommendations for corticosteroid therapy are in accordance with the national practice parameters developed by the American Academy of Neurology and the Child Neurology Society [Moxley et al 2005] (full text), as well as the DMD Care Considerations Working Group [Bushby et al 2010a].
=== Secondary Prevention ===


* Boys with DMD should be offered treatment with prednisone (0.75 mg/kg/day, maximum daily dose: 30-40 mg) or deflazacort (0.9 mg/kg/day, maximum daily dose: 36-39 mg) as soon as plateauing or decline in motor skills is noted, which usually occurs at age 4-8 years. Prior to the initiation of therapy, the potential benefits and risks of corticosteroid treatment should be carefully discussed with each individual.
* Once diagnosed, patients with Becker's muscular [[dystrophy]] are followed-up every year or two years by [[cardiology]]. Follow-up testing includes [[pulmonary function tests]], measurement of [[scoliosis]], wheelchair depence, and [[cardiac assesment]].<ref name="pmid2030129817" />
* To assess benefits of corticosteroid therapy, the following parameters are useful: timed muscle function tests, pulmonary function tests, and age at loss of independent ambulation.
*Annual [[Influenza vaccine|influenza]] and [[Pneumococcal Vaccine 13-Valent|pneumococcal]] vaccines should be given, as well [[vitamin D]] and [[calcium]] to prevent fractures.<ref name="pmid2030129817" />
* To assess risks of corticosteroid therapy, maintain awareness of the potential corticosteroid therapy side effects (e.g., weight gain, cushingoid appearance, short stature, decrease in linear growth, acne, excessive hair growth, gastrointestinal symptoms, behavioral changes). There is also an increased frequency of vertebral and long bone fractures with prolonged corticosteroid use [King et al 2007].
* The optimal maintenance dose of prednisone (0.75 mg/kg/day) or deflazacort (0.9 mg/kg/day) should be continued if side effects are not severe. Significant but less robust improvement can be seen with gradual tapering of prednisone to as low as 0.3 mg/kg/day (or ~0.4 mg/kg/day of deflazacort).
* If excessive weight gain occurs (>20% over estimated normal weight for height over a 12-month period), the prednisone dose should be decreased by 25%-33% and reassessed in a few months. If excessive weight gain continues, the dose should be further decreased by an additional 25% to the minimum effective dose cited above after three to four months.
* If significant weight gain or intolerable behavioral side effects occur in patients treated with prednisone, change to deflazacort on a ten-day-on / ten-day-off schedule or a high-dose weekend schedule. In patients on deflazacort, side effects of asymptomatic cataracts and weight gain should be monitored.


'''BMD.''' Information about the efficacy of prednisone in treating individuals with BMD is limited. Many clinicians continue treatment with glucocorticoids after loss of ambulation for the purpose of maintaining upper limb strength, delaying the progressive decline of respiratory and cardiac function, and decreasing the risk of scoliosis. Retrospective data suggest that the progression of scoliosis can be reduced by long-term daily corticosteroid treatment; however, an increased risk for vertebral and lower-limb fractures has been documented [King et al 2007]. Men on steroid therapy were less likely to require spinal surgery [Dooley et al 2010b]. The dose is allowed to drift down to 0.3-0.6 mg/kg/day of prednisone or deflazacort, which is still effective [Bushby et al 2010a].<ref name="pmid170419063">{{cite journal| author=Deburgrave N, Daoud F, Llense S, Barbot JC, Récan D, Peccate C | display-authors=etal| title=Protein- and mRNA-based phenotype-genotype correlations in DMD/BMD with point mutations and molecular basis for BMD with nonsense and frameshift mutations in the DMD gene. | journal=Hum Mutat | year= 2007 | volume= 28 | issue= 2 | pages= 183-95 | pmid=17041906 | doi=10.1002/humu.20422 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17041906  }}</ref>
{{Muscular Dystrophy}}<br />
 
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[[it:Distrofia muscolare di Becker]]
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[[nl:Becker spierdystrofie]]
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Moises Romo, M.D.

Overview

Former "pseudohypertrophic muscular dystrophy", now Becker's muscular dystrophy, is a genetic neuromuscular condition characterized by slowly progresive weakness and atrophy of skeletal (mostly legs and pelvis) and cardiac muscles.

Historical Perspective

Pathophysiology

Clinical Features

Unlike Duchenne muscular dystrophy, Becker's muscular dystrophy (BMD) phenotype presents at a later age, widely variable onset from early childhood to late adulthood, most of them falling in puberty range. Most of the patients will requiere a wheelchair after age 16.[12]

Clinical presentation Becker's muscular dystrophy include:

There is an abcense of fasciculations, and this finding may exclude BMD[13][14]

CNS is rarely afected in Becker's muscular dystrophy, for this reason, intelligence is usually spared.[12][17]

Most of women are asymptomatic carriers, with very rare cases presenting the classic symptoms.[12][9]

Differentiating Becker's muscular dystrophy from other Diseases

Becker's muscular dystrophy must be differentiated from other diseases that cause skelletal and cardiac muscle afection, such as:

Screening


Epidemiology and Demographics

  • The prevalence of Becker's muscular dystrophy is approximately 1-3 per 100,000 individuals.
  • The incidence of Becker's muscular dystrophy is approximately 3-6 per 100,000 male births worldwide.

Age

Becker's muscular dystrophy is diagnosed in 85% of patients by age 25.[21]

Gender

Becker's muscular dystrophy affects mostly men, women are carriers almost exclusively (except rare situation).[22]

Race

  • Becker's muscular dystrophy usually affects individuals of the hispanic race.[23][24]
  • Asian individuals are less likely to develop Becker's muscular dystrophy.[23][24]

Risk Factors

Natural History, Complications and Prognosis


Diagnosis

The diagnosis of Becker's muscular dystrophy is made with a classic clinical presentation plus elevated CK, molecular genetic testing, or muscle biopsy.[33]

Symptoms

Symptoms of Becker's muscular dystrophy may include the following:

Physical Examination

Patients with Becker's muscular dystrophy usually adopt a posture with shoulders held back, abdomen stuck out, and lumbar hyperlordosis.[34]

Physical examination may be remarkable for:

Laboratory Findings

An elevated CK is typical in Becker's muscular dystrophy, with a peak around 10-15 years of age.[35]

Other laboratory findings consistent with Becker's muscular dystrophy may be:

Hystopathology

Histologic findings in Becker's muscular may be:

EMG

EMG in Becker's muscular dystrophy, may reveal myopathic motor units with or without muscle membrane instability.[35][38]

Echocardiography

Echocardiogram should be done at the time of diagnosis.[38][39]

Imaging Findings

There are no X-ray findings characteristic with with Becker's muscular dystrophy, but scoliosis may be found.[34]

Treatment

Medical Therapy

Surgery

Primary Prevention

There are no primary preventive measures available for Becker's muscular dystrophy.[31]

Secondary Prevention

Template:Muscular Dystrophy

References


==References== 

{{Reflist|2}}

  1. ↑ Zeidman LA, Kondziella D (April 2014). "Peter Becker and his Nazi past: the man behind Becker muscular dystrophy and Becker myotonia". J. Child Neurol. 29 (4): 514–9. doi:10.1177/0883073813482773. PMID 23576413.
  2. ↑ "Guillaume Benjamin Amand Duchenne de Boulogne".
  3. ↑ Mercuri E, Bönnemann CG, Muntoni F (November 2019). "Muscular dystrophies". Lancet. 394 (10213): 2025–2038. doi:10.1016/S0140-6736(19)32910-1. PMID 31789220.
  4. ↑ 4.0 4.1 Hoffman, Eric P.; Brown, Robert H.; Kunkel, Louis M. (1987). "Dystrophin: The protein product of the duchenne muscular dystrophy locus". Cell. 51 (6): 919–928. doi:10.1016/0092-8674(87)90579-4. ISSN 0092-8674.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Sarkozy, A.; Bushby, K.; Mercuri, E. (2014). "Muscular Dystrophies". doi:10.1016/B978-0-12-801238-3.05597-5.
  6. ↑ "Becker muscular dystrophy | Genetic and Rare Diseases Information Center (GARD) – an NCATS Program".
  7. ↑ 7.0 7.1 Wicklund MP (December 2013). "The muscular dystrophies". Continuum (Minneap Minn). 19 (6 Muscle Disease): 1535–70. doi:10.1212/01.CON.0000440659.41675.8b. PMID 24305447.
  8. ↑ Iannaccone, Susan T.; Castro, Diana (2013). "Congenital Muscular Dystrophies and Congenital Myopathies". CONTINUUM: Lifelong Learning in Neurology. 19: 1509–1534. doi:10.1212/01.CON.0000440658.03557.f1. ISSN 1080-2371.
  9. ↑ 9.0 9.1 Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean L, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS. PMID 20301298. Vancouver style error: initials (help); Missing or empty |title= (help)
  10. ↑
  11. ↑ Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean L, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS. PMID 20301298. Vancouver style error: initials (help); Missing or empty |title= (help)
  12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean L, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS. PMID 20301298. Vancouver style error: initials (help); Missing or empty |title= (help)
  13. ↑ 13.0 13.1 13.2 Sarkozy, A.; Bushby, K.; Mercuri, E. (2014). "Muscular Dystrophies". doi:10.1016/B978-0-12-801238-3.05597-5.
  14. ↑ 14.0 14.1 14.2 Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean L, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS. PMID 20301298. Vancouver style error: initials (help); Missing or empty |title= (help)
  15. ↑ 15.0 15.1 Wicklund MP (December 2013). "The muscular dystrophies". Continuum (Minneap Minn). 19 (6 Muscle Disease): 1535–70. doi:10.1212/01.CON.0000440659.41675.8b. PMID 24305447.
  16. ↑ 16.0 16.1 16.2 16.3 16.4 16.5
  17. ↑ Sarkozy, A.; Bushby, K.; Mercuri, E. (2014). "Muscular Dystrophies". doi:10.1016/B978-0-12-801238-3.05597-5.
  18. ↑ 18.0 18.1 Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean L, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS. PMID 20301298. Vancouver style error: initials (help); Missing or empty |title= (help)
  19. ↑ 19.0 19.1 Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean L, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS. PMID 20301298. Vancouver style error: initials (help); Missing or empty |title= (help)
  20. ↑ 20.0 20.1 Deburgrave N, Daoud F, Llense S, Barbot JC, Récan D, Peccate C, Burghes AH, Béroud C, Garcia L, Kaplan JC, Chelly J, Leturcq F (February 2007). "Protein- and mRNA-based phenotype-genotype correlations in DMD/BMD with point mutations and molecular basis for BMD with nonsense and frameshift mutations in the DMD gene". Hum. Mutat. 28 (2): 183–95. doi:10.1002/humu.20422. PMID 17041906.
  21. ↑ Bushby KM, Thambyayah M, Gardner-Medwin D (April 1991). "Prevalence and incidence of Becker muscular dystrophy". Lancet. 337 (8748): 1022–4. doi:10.1016/0140-6736(91)92671-n. PMID 1673177.
  22. ↑ Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean L, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS. PMID 20301298. Vancouver style error: initials (help); Missing or empty |title= (help)
  23. ↑ 23.0 23.1 "Prevalence of Duchenne / Becker Muscular Dystrophies | CDC".
  24. ↑ 24.0 24.1 "Prevalence of Duchenne/Becker muscular dystrophy among males aged 5-24 years - four states, 2007". MMWR Morb. Mortal. Wkly. Rep. 58 (40): 1119–22. October 2009. PMID 19834452.
  25. ↑ "Prevalence of Duchenne/Becker muscular dystrophy among males aged 5-24 years - four states, 2007". MMWR Morb. Mortal. Wkly. Rep. 58 (40): 1119–22. October 2009. PMID 19834452.
  26. ↑ Barakat-Haddad C, Shin S, Candundo H, Lieshout PV, Martino R (July 2017). "A systematic review of risk factors associated with muscular dystrophies". Neurotoxicology. 61: 55–62. doi:10.1016/j.neuro.2016.03.007. PMID 27018093.
  27. ↑ 27.0 27.1 Emery AE, Skinner R (October 1976). "Clinical studies in benign (Becker type) X-linked muscular dystrophy". Clin. Genet. 10 (4): 189–201. doi:10.1111/j.1399-0004.1976.tb00033.x. PMID 975594.
  28. ↑ 28.0 28.1 Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean L, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS. PMID 20301298. Vancouver style error: initials (help); Missing or empty |title= (help)
  29. ↑ 29.0 29.1 29.2 29.3 29.4 Passamano L, Taglia A, Palladino A, Viggiano E, D'Ambrosio P, Scutifero M, Rosaria Cecio M, Torre V, DE Luca F, Picillo E, Paciello O, Piluso G, Nigro G, Politano L (October 2012). "Improvement of survival in Duchenne Muscular Dystrophy: retrospective analysis of 835 patients". Acta Myol. 31 (2): 121–5. PMC 3476854. PMID 23097603.
  30. ↑ 30.00 30.01 30.02 30.03 30.04 30.05 30.06 30.07 30.08 30.09 30.10 30.11 "www.mda.org" (PDF).
  31. ↑ 31.0 31.1 31.2 31.3 31.4 "Pathology Outlines - Becker muscular dystrophy".
  32. ↑ Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean L, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS. PMID 20301298. Vancouver style error: initials (help); Missing or empty |title= (help)
  33. ↑ 33.0 33.1 33.2 33.3 33.4 33.5 Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean L, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS. PMID 20301298. Vancouver style error: initials (help); Missing or empty |title= (help)
  34. ↑ 34.0 34.1 Smith AD, Koreska J, Moseley CF (August 1989). "Progression of scoliosis in Duchenne muscular dystrophy". J Bone Joint Surg Am. 71 (7): 1066–74. PMID 2760082.
  35. ↑ 35.0 35.1 35.2 Wicklund MP (December 2013). "The muscular dystrophies". Continuum (Minneap Minn). 19 (6 Muscle Disease): 1535–70. doi:10.1212/01.CON.0000440659.41675.8b. PMID 24305447.
  36. ↑ Deburgrave N, Daoud F, Llense S, Barbot JC, Récan D, Peccate C, Burghes AH, Béroud C, Garcia L, Kaplan JC, Chelly J, Leturcq F (February 2007). "Protein- and mRNA-based phenotype-genotype correlations in DMD/BMD with point mutations and molecular basis for BMD with nonsense and frameshift mutations in the DMD gene". Hum. Mutat. 28 (2): 183–95. doi:10.1002/humu.20422. PMID 17041906.
  37. ↑ Lee SH, Lee JH, Lee KA, Choi YC (July 2015). "Clinical and Genetic Characterization of Female Dystrophinopathy". J Clin Neurol. 11 (3): 248–51. doi:10.3988/jcn.2015.11.3.248. PMC 4507379. PMID 26022459.
  38. ↑ 38.0 38.1 Naddaf E, Milone M, Mauermann ML, Mandrekar J, Litchy WJ (2018). "Muscle Biopsy and Electromyography Correlation". Front Neurol. 9: 839. doi:10.3389/fneur.2018.00839. PMC 6189315. PMID 30356714.
  39. ↑ 39.0 39.1 39.2 39.3 39.4 39.5 39.6 Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean L, Stephens K, Amemiya A, Darras BT, Urion DK, Ghosh PS. PMID 20301298. Vancouver style error: initials (help); Missing or empty |title= (help)
  40. ↑ 40.0 40.1 Sarkozy, A.; Bushby, K.; Mercuri, E. (2014). "Muscular Dystrophies". doi:10.1016/B978-0-12-801238-3.05597-5.
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