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{{CMG}}; {{AE}} {{AN}} {{shyam}}
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==Overview==
==Overview==
'''Sickle-cell disease''' is a group of [[genetic disorders]] of the [[red blood cell]] caused by a mutation in the β-globin chain gene of [[hemoglobin]] at the 6th position replacing [[glutamic acid]] to [[valine]]. HbS polymerizes reversibly when deoxygenated to form a network of fibrous [[hemoglobin]] polymers that stiffens the RBC [[Cell membrane|membrane]], giving it a sickle shape. These sickled cells loose the pliability to cross thin capillaries and possess a sticky membrane, giving it a property to adhere to the [[endothelium]] of blood vessels, thereby causing vaso-occlusion. It causes significant morbidity and mortality, particularly in people in the Mediterranean and African region.
'''Sickle-cell disease''' is a group of [[genetic disorders]] of the [[red blood cell]] caused by a mutation in the β-globin chain gene of [[hemoglobin]] at the 6th position replacing [[glutamic acid]] to [[valine]]. HbS polymerizes reversibly when deoxygenated to form a network of fibrous [[hemoglobin]] polymers that stiffens the RBC [[Cell membrane|membrane]], giving it a sickle shape. These sickled cells loose the pliability to cross thin capillaries and possess a sticky membrane, giving it a property to adhere to the [[endothelium]] of blood vessels, thereby causing vaso-occlusion. It causes significant morbidity and mortality, particularly in people in the Mediterranean and African region. The treatment includes measures to avoid vaso-occlusion, such as avoidance of dehydration, low oxygen conditions, or cold weather. Hydroxyurea has been used to increase fetal hemoglobin production.


==Historical Perspective==
==Historical Perspective==
*Sickle cell disease has a significant historical perspective. Many centuries ago, it was noted that people from Africa succumbed to vaso-occlusive pain crises.<ref name="pmid19610078">{{cite journal| author=Kato GJ, Hebbel RP, Steinberg MH, Gladwin MT| title=Vasculopathy in sickle cell disease: Biology, pathophysiology, genetics, translational medicine, and new research directions. | journal=Am J Hematol | year= 2009 | volume= 84 | issue= 9 | pages= 618-25 | pmid=19610078 | doi=10.1002/ajh.21475 | pmc=3209715 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19610078  }} </ref> At this time, the etiology for pain crises was not clear. The pioneering work established by James Herrick nearly a century years ago. James Herrick noted that a dental student from Grenada had abnormally shaped rec blood cells on his peripheral blood smear. In 1936, vaso-occlusion the pulmonary vascular beds was noted on an autopsy.<ref name="pmid19610078">{{cite journal| author=Kato GJ, Hebbel RP, Steinberg MH, Gladwin MT| title=Vasculopathy in sickle cell disease: Biology, pathophysiology, genetics, translational medicine, and new research directions. | journal=Am J Hematol | year= 2009 | volume= 84 | issue= 9 | pages= 618-25 | pmid=19610078 | doi=10.1002/ajh.21475 | pmc=3209715 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19610078  }} </ref> It was not until 1949 that sickle cell disease was associated with an alteration of hemoglobin. Linus Pauling and coworkers noted for the first time that a genetic disease was linked to a mutation of a specific protein.  
Sickle-cell disease was first discovered by [[James Herrick]], an American cardiologist and professor of medicine, in 1910 following presentation by his intern Ernest Irons.<ref name="pmid19610078">{{cite journal| author=Kato GJ, Hebbel RP, Steinberg MH, Gladwin MT| title=Vasculopathy in sickle cell disease: Biology, pathophysiology, genetics, translational medicine, and new research directions. | journal=Am J Hematol | year= 2009 | volume= 84 | issue= 9 | pages= 618-25 | pmid=19610078 | doi=10.1002/ajh.21475 | pmc=3209715 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19610078  }} </ref> In 1922, the phrase, "sickle-cell anemia," was first used by Verne Mason, M.D. at Johns Hopkins University to describe the shape of the red blood cells.


==Classification==
==Classification==
*Sickle cell disease does not have a traditional classification method, as is true for other hemoglobinopathies.<ref name="pmid23378597">{{cite journal| author=Forget BG, Bunn HF| title=Classification of the disorders of hemoglobin. | journal=Cold Spring Harb Perspect Med | year= 2013 | volume= 3 | issue= 2 | pages= a011684 | pmid=23378597 | doi=10.1101/cshperspect.a011684 | pmc=3552344 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23378597  }} </ref> However, there are a few particular subtypes. Each subtype is based on the number and type of hemoglobin allele(s). The letter S denotes an allele with the sickle cell mutation. The subtypes (and the associated disease in parentheses below) are as follows:
Sickle-cell disease may be classified according to the number and type of the two alleles of beta-globin. Sickle-cell disease may also be classified as an [[autosomal recessive]] genetic disorder. Sickle cell disease does not have a traditional classification method, as is true for other hemoglobinopathies.<ref name="pmid23378597">{{cite journal| author=Forget BG, Bunn HF| title=Classification of the disorders of hemoglobin. | journal=Cold Spring Harb Perspect Med | year= 2013 | volume= 3 | issue= 2 | pages= a011684 | pmid=23378597 | doi=10.1101/cshperspect.a011684 | pmc=3552344 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23378597  }} </ref> However, there are a few particular subtypes. Each subtype is based on the number and type of hemoglobin allele(s). The letter S denotes an allele with the sickle cell mutation. The subtypes (and the associated disease in parentheses below) are as follows:
:*HbSS (sickle cell anemia)
:*HbSS (sickle cell anemia)
:*HbSC (milder form of sickle cell anemia)
:*HbSC (milder form of sickle cell anemia)
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.
.
==Pathophysiology==
==Pathophysiology==
*The pathogenesis of sickle cell disease is characterized by an amino acid substitution on the beta-globin chain on chromosome 11, resulting in red blood cell sickling and vaso-occlusive episodes in various organs.
The pathophysiology of sickle cell disease is based on a mutation in the beta-globin chain of hemoglobin, which leads to red blood cell sickling and vaso-occlusive crises. The pathogenesis of sickle cell disease is characterized by an amino acid substitution on the beta-globin chain on chromosome 11, resulting in red blood cell sickling and vaso-occlusive episodes in various organs. A mutation in beta-globin, namely a a point mutation in exon 1 that substitutes valine for glutamic acid, has been associated with the development of sickle cell disease, involving the [[hemoglobin]] synthesis pathway.<ref name="pmid22924029">{{cite journal| author=Ballas SK, Kesen MR, Goldberg MF, Lutty GA, Dampier C, Osunkwo I et al.| title=Beyond the definitions of the phenotypic complications of sickle cell disease: an update on management. | journal=ScientificWorldJournal | year= 2012 | volume= 2012 | issue=  | pages= 949535 | pmid=22924029 | doi=10.1100/2012/949535 | pmc=3415156 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=22924029  }} </ref> On microscopic analysis, a peripheral blood smear will show sickle-shaped red blood cells, which are the characteristic findings of sickle cell disease. In some cases, hemoglobin C crystals may be observed. The point mutation causes cells to sickle, resulting in decreased deformability and decreased passage of red blood cells through the vasculature.<ref name="pmid27063958">{{cite journal| author=Alapan Y, Kim C, Adhikari A, Gray KE, Gurkan-Cavusoglu E, Little JA et al.| title=Sickle cell disease biochip: a functional red blood cell adhesion assay for monitoring sickle cell disease. | journal=Transl Res | year= 2016 | volume= 173 | issue=  | pages= 74-91.e8 | pmid=27063958 | doi=10.1016/j.trsl.2016.03.008 | pmc=4959913 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=27063958  }} </ref>
*A mutation in beta-globin, namely a a point mutation in exon 1 that substitutes valine for glutamic acid has been associated with the development of sickle cell disease, involving the [[hemoglobin]] synthesis pathway.<ref name="pmid22924029">{{cite journal| author=Ballas SK, Kesen MR, Goldberg MF, Lutty GA, Dampier C, Osunkwo I et al.| title=Beyond the definitions of the phenotypic complications of sickle cell disease: an update on management. | journal=ScientificWorldJournal | year= 2012 | volume= 2012 | issue=  | pages= 949535 | pmid=22924029 | doi=10.1100/2012/949535 | pmc=3415156 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=22924029  }} </ref>
Gross pathology does not play a significant role in diagnosis.
On microscopic analysis, a peripheral blood smear will show sickle-shaped red blood cells, which are the characteristic findings of sickle cell disease. In some cases, hemoglobin C crystals can be seen.


==Causes==
==Causes==
* Sickle cell disease is caused by a mutation in the beta-globin gene on chromosome 11.
Sickle cell disease is caused by a mutation in the beta-globin gene on chromosome 11.
* There are no other established causes for sickle cell disease.


==Differentiating Sickle Cell Disease from other Diseases==
==Differentiating Sickle Cell Disease from other Diseases==
*Sickle cell disease must be differentiated from other diseases that cause fatigue, infection, bone pain, such as:
*Sickle cell disease must be differentiated from other diseases that cause [[fatigue]], infection, [[bone pain]], such as:<ref name="pmid19885711">{{cite journal| author=Hernigou P, Daltro G, Flouzat-Lachaniette CH, Roussignol X, Poignard A| title=Septic arthritis in adults with sickle cell disease often is associated with osteomyelitis or osteonecrosis. | journal=Clin Orthop Relat Res | year= 2010 | volume= 468 | issue= 6 | pages= 1676-81 | pmid=19885711 | doi=10.1007/s11999-009-1149-3 | pmc=2865595 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19885711  }} </ref><ref name="pmid25742458">{{cite journal| author=Sankaran VG, Weiss MJ| title=Anemia: progress in molecular mechanisms and therapies. | journal=Nat Med | year= 2015 | volume= 21 | issue= 3 | pages= 221-30 | pmid=25742458 | doi=10.1038/nm.3814 | pmc=4452951 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=25742458  }} </ref>
:*[[Thalassemia]]
:*[[Thalassemia]]
:*Acute [[leukemia]]
:*Acute [[leukemia]]
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===Race===
===Race===
*There is a racial predilection for sickle cell disease.
*There is a racial predilection for sickle cell disease.
**Sickle cell disease usually affects individuals of the black race.
*Sickle cell disease usually affects individuals of the black race.
**Sickle cell disease also affects persons of eastern Mediterranean descent and Middle Eastern descent.
*Sickle cell disease also affects persons of eastern Mediterranean descent and Middle Eastern descent.


==Risk Factors==
==Risk Factors==
*There are no other risk factors (aside from race) in the development of sickle cell disease. There are, however, risk factors for precipitation of painful vaso-occlusive crises, such as dehydration and poor oxygenation. Risk factors for development of overt renal failure include hypertension, [[hematuria]], nephrotic-range proteinuria, and severe anemia.
The most potent risk factor in the development of sickle-cell disease is race, which include Africans, African Americans, Indians, and persons of Mediterranean descent. An additional risk factor is geographic location, with these locations containing the greatest occurrences of disease.<ref name="pmid25143960">{{cite journal| author=Makani J, Ofori-Acquah SF, Nnodu O, Wonkam A, Ohene-Frempong K| title=Sickle cell disease: new opportunities and challenges in Africa. | journal=ScientificWorldJournal | year= 2013 | volume= 2013 | issue=  | pages= 193252 | pmid=25143960 | doi=10.1155/2013/193252 | pmc=3988892 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=25143960  }} </ref>
   
   
==Screening==
Sickle cell disease is currently a disease for which newborn screening is available, mandated, and routinely performed in the United States.<ref name="pmid21927581">{{cite journal| author=Brandow AM, Liem R| title="Sickle Cell Disease in the Emergency Department: Atypical Complications and Management" | journal=Clin Pediatr Emerg Med | year= 2011 | volume= 12 | issue= 3 | pages= 202-212 | pmid=21927581 | doi=10.1016/j.cpem.2011.07.003 | pmc=3172721 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21927581  }} </ref>
== Natural History, Complications and Prognosis==
== Natural History, Complications and Prognosis==
*The majority of patients with sickle cell disease remain asymptomatic until the second half of the first year of life. This is the time when fetal hemoglobin production declines such that sickled hemoglobin manifests clinically.  
*The majority of patients with sickle cell disease remain asymptomatic until the second half of the first year of life. This is the time when fetal hemoglobin production declines such that sickled hemoglobin manifests clinically.  
*Early clinical features include painful crises, fatigue, and shortness of breath.
*If left untreated, sickle-cell disease can result in death.
*Common complications of sepsis, hypoxia, tissue infarction, and death.
*Early clinical features include painful crises, [[fatigue]], and [[shortness of breath]].
*Prognosis is generally guarded, and the survival rate at age 18 years rate is approximately 94%, in a Dallas newborn cohort. In Africa, many children are left undiagnosed, so the survival rate is lower.
*Common complications include [[sepsis]], [[hypoxia]], tissue infarction, depression, and death.<ref name="pmid12911250">{{cite journal| author=Hasan SP, Hashmi S, Alhassen M, Lawson W, Castro O| title=Depression in sickle cell disease. | journal=J Natl Med Assoc | year= 2003 | volume= 95 | issue= 7 | pages= 533-7 | pmid=12911250 | doi= | pmc=2594635 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12911250  }} </ref>
*Prognosis is generally guarded in the United States and poor in developing nations.
   
   
== Diagnosis ==
== Diagnosis ==
===Diagnostic Criteria===
===Diagnostic Criteria===
*The diagnosis of sickle cell disease is made when a person has:
*The diagnosis of sickle cell disease is made when a person has:
:*the characteristic genetic mutation (glutamic acid to valine) in beta-globin
:*The characteristic genetic mutation (glutamic acid to valine) in beta-globin
:*symptoms characteristic of sickle cell disease
:*Symptoms characteristic of sickle cell disease
   
   
=== Symptoms ===
=== Symptoms ===
*Sickle cell disease is usually symptomatic.
*Sickle cell disease is usually symptomatic.
*Symptoms of sickle cell disease may include the following:
Symptoms of sickle-cell disease include:
:*Bone pain
*[[Pain and nociception|Pain]] and/or [[bone pain]]
:*Fever
*[[Dactylitis]]
:*Infection
*[[Blurry vision]]
:*Chest pain
*[[priapism|Persistent and painful erection]]
:*Blurry vision
*[[Numbness]]
:*Fatigue
*[[Tingling]]
:*Shortness of breath
*Motor skill loss
*[[aphasia|Speech deficits]]
*[[Gait disturbance]]
*Leg ulceration
*[[Jaundice]]
   
   
=== Physical Examination ===
=== Physical Examination ===
*Patients with sickle cell disease usually appear ill during times of acute exacerbation of painful crises. If patients are well controlled on their medications, they can appear clinically well.
*Patients with sickle cell disease usually appear ill during times of acute exacerbation of painful crises. If patients are well controlled on their medications, they can appear clinically well.
*Physical examination may be remarkable for:
*Physical examination may be remarkable for:
:*Hypotension
:*[[Hypotension]]
:*Tachycardia
:*[[Tachycardia]]
:*Dehydration
:*[[Dehydration]]
:*Scleral icterus
:*Scleral icterus
:*Pallor (conjunctival, mucosal, and/or skin)
:*[[Pallor]] (conjunctival, mucosal, and/or skin)
:*Fever
:*[[Fever]]
:*Otitis/sinusitis
:*[[Otitis]]/[[sinusitis]]
:*Splenomegaly (due to extramedullary hematopoiesis)
:*[[Splenomegaly]] (due to extramedullary hematopoiesis)
:*Heart failure
:*[[Heart failure]]
:*Frontal and parietal bone bossing (due to extramedullary hematopoiesis)
:*Frontal and parietal bone bossing (due to extramedullary hematopoiesis)
   
   
=== Laboratory Findings ===
=== Laboratory Findings ===
*There are some specific laboratory findings associated with sickle cell disease.  
The most important laboratory test for sickle cell anemia is a complete blood count (CBC), specifically [[hemoglobin]] and [[hematocrit]]. Low hemoglobin (anemia) is due to the intrinsic nature of the disease. A positive peripheral blood smear showing sickle-shaped cells is characteristic of sickle cell disease. High total bilirubin with predominantly indirect bilirubin may suggest hemolysis, since bilirubin is a breakdown production of hemoglobin. High lactate dehydrogenase (LDH) may also be seen if there is hemolysis. High reticulocyte count may be seen if the bone marrow is attempting to compensate for the anemia. Low oxygen content on arterial blood gas (ABG) may be observed.
Low hemoglobin (anemia) is due to the intrinsic nature of the disease.
High total bilirubin with predominantly indirect bilirubin may suggest hemolysis, since bilirubin is a breakdown production of hemoglobin. High lactate dehydrogenase (LDH) may also be seen if there is hemolysis.
High reticulocyte count may be seen if the bone marrow is attempting to compensate for the anemia.
Low oxygen content on arterial blood gas (ABG) may be seen.
 
*A positive peripheral blood smear showing sickle-shaped cells is characteristic of sickle cell disease.
   
   
===Imaging Findings===
===Imaging Findings===
In some cases, plain imaging such as X-rays can be useful. These can show subacute of chronic infarcts of the extremities. Deformities may also be seen on plain radiogrpahs.  
*In some cases, plain imaging such as x ray can be useful, which may reveal subacute or chronic infarcts of the extremities or deformities.
*CT scan is useful for patients with suspected stroke due to vaso-occlusion.
*MRI can show avascular necrosis of the leg. It can also show [[osteomyelitis]] and marrow hyperplasia.
*MRI can show avascular necrosis of the leg. It can also show [[osteomyelitis]] and marrow hyperplasia.
*CT scan is useful for patients with suspected stroke due to vaso-occlusion.
   
   
=== Other Diagnostic Studies ===
=== Other Diagnostic Studies ===
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=== Prevention ===
=== Prevention ===
*There are no primary preventive measures available for sickle cell disease. However, genetic counseling is an option. Two mates with sickle cell trait have a 25% chance of producing an offspring with sickle cell disease. For a patient with sickle cell disease who has a baby, the patient's partner should be tested to given insight into the baby's sickle cell status.
*There are no primary preventive measures available for sickle cell disease. However, genetic counseling is an option.


Hydroxyurea can prevent sickle cell crises by increasing fetal hemoglobin. Fetal hemoglobin protects against complications of anemia.<ref name="pmid23465615">{{cite journal| author=Ngo D, Bae H, Steinberg MH, Sebastiani P, Solovieff N, Baldwin CT et al.| title=Fetal hemoglobin in sickle cell anemia: genetic studies of the Arab-Indian haplotype. | journal=Blood Cells Mol Dis | year= 2013 | volume= 51 | issue= 1 | pages= 22-6 | pmid=23465615 | doi=10.1016/j.bcmd.2012.12.005 | pmc=3647015 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23465615  }} </ref>
Hydroxyurea can prevent sickle cell crises by increasing fetal hemoglobin. Fetal hemoglobin protects against complications of anemia.<ref name="pmid23465615">{{cite journal| author=Ngo D, Bae H, Steinberg MH, Sebastiani P, Solovieff N, Baldwin CT et al.| title=Fetal hemoglobin in sickle cell anemia: genetic studies of the Arab-Indian haplotype. | journal=Blood Cells Mol Dis | year= 2013 | volume= 51 | issue= 1 | pages= 22-6 | pmid=23465615 | doi=10.1016/j.bcmd.2012.12.005 | pmc=3647015 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23465615  }} </ref><ref name="pmid26576059">{{cite journal| author=Fitzhugh CD, Hsieh MM, Allen D, Coles WA, Seamon C, Ring M et al.| title=Hydroxyurea-Increased Fetal Hemoglobin Is Associated with Less Organ Damage and Longer Survival in Adults with Sickle Cell Anemia. | journal=PLoS One | year= 2015 | volume= 10 | issue= 11 | pages= e0141706 | pmid=26576059 | doi=10.1371/journal.pone.0141706 | pmc=4648496 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=26576059  }} </ref>
*Effective measures for the primary prevention of sickle cell disease include screening. Once sickle cell disease is present, preventive measures to avoid sickling and vaso-cclusive crises include hydration and oxygenation.


==References==
==References==
{{reflist|2}}
{{reflist|2}}


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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aarti Narayan, M.B.B.S [2], Shyam Patel [3]

Overview

Sickle-cell disease is a group of genetic disorders of the red blood cell caused by a mutation in the β-globin chain gene of hemoglobin at the 6th position replacing glutamic acid to valine. HbS polymerizes reversibly when deoxygenated to form a network of fibrous hemoglobin polymers that stiffens the RBC membrane, giving it a sickle shape. These sickled cells loose the pliability to cross thin capillaries and possess a sticky membrane, giving it a property to adhere to the endothelium of blood vessels, thereby causing vaso-occlusion. It causes significant morbidity and mortality, particularly in people in the Mediterranean and African region. The treatment includes measures to avoid vaso-occlusion, such as avoidance of dehydration, low oxygen conditions, or cold weather. Hydroxyurea has been used to increase fetal hemoglobin production.

Historical Perspective

Sickle-cell disease was first discovered by James Herrick, an American cardiologist and professor of medicine, in 1910 following presentation by his intern Ernest Irons.[1] In 1922, the phrase, "sickle-cell anemia," was first used by Verne Mason, M.D. at Johns Hopkins University to describe the shape of the red blood cells.

Classification

Sickle-cell disease may be classified according to the number and type of the two alleles of beta-globin. Sickle-cell disease may also be classified as an autosomal recessive genetic disorder. Sickle cell disease does not have a traditional classification method, as is true for other hemoglobinopathies.[2] However, there are a few particular subtypes. Each subtype is based on the number and type of hemoglobin allele(s). The letter S denotes an allele with the sickle cell mutation. The subtypes (and the associated disease in parentheses below) are as follows:

  • HbSS (sickle cell anemia)
  • HbSC (milder form of sickle cell anemia)
  • HbAS (sickle cell trait)
  • HbSB+thal (beta-thalassemia anemia)
  • HbSB0thal (beta-thalassemia anemia)
  • Other variants of sickle cell disease include HbSD, HbSE, or HbSO (one sickle cell gene and one other gene).[2]

.

Pathophysiology

The pathophysiology of sickle cell disease is based on a mutation in the beta-globin chain of hemoglobin, which leads to red blood cell sickling and vaso-occlusive crises. The pathogenesis of sickle cell disease is characterized by an amino acid substitution on the beta-globin chain on chromosome 11, resulting in red blood cell sickling and vaso-occlusive episodes in various organs. A mutation in beta-globin, namely a a point mutation in exon 1 that substitutes valine for glutamic acid, has been associated with the development of sickle cell disease, involving the hemoglobin synthesis pathway.[3] On microscopic analysis, a peripheral blood smear will show sickle-shaped red blood cells, which are the characteristic findings of sickle cell disease. In some cases, hemoglobin C crystals may be observed. The point mutation causes cells to sickle, resulting in decreased deformability and decreased passage of red blood cells through the vasculature.[4]

Causes

Sickle cell disease is caused by a mutation in the beta-globin gene on chromosome 11.

Differentiating Sickle Cell Disease from other Diseases

  • Sickle cell disease must be differentiated from other diseases that cause fatigue, infection, bone pain, such as:[5][6]

Epidemiology and Demographics

  • The prevalence of sickle cell disease is approximately 160 per 100,000 individuals worldwide at birth. The actual prevalence, however, is less given that people die from the disease at an early time point.
  • Approximately 1 in 12 persons of African descent have sickle cell trait.
  • Approximately 100,000 persons are living with sickle cell disease in the United States.

Age

  • Age is not a risk factor for sickle cell disease since this disease is inherited at birth. Unlike other diseases that increase with age, persons with sickle cell disease are born with the condition.

Gender

  • Sickle cell disease affects men and women equally. It is not an X-linked disease.

Race

  • There is a racial predilection for sickle cell disease.
    • Sickle cell disease usually affects individuals of the black race.
    • Sickle cell disease also affects persons of eastern Mediterranean descent and Middle Eastern descent.

Risk Factors

The most potent risk factor in the development of sickle-cell disease is race, which include Africans, African Americans, Indians, and persons of Mediterranean descent. An additional risk factor is geographic location, with these locations containing the greatest occurrences of disease.[7]

Screening

Sickle cell disease is currently a disease for which newborn screening is available, mandated, and routinely performed in the United States.[8]

Natural History, Complications and Prognosis

  • The majority of patients with sickle cell disease remain asymptomatic until the second half of the first year of life. This is the time when fetal hemoglobin production declines such that sickled hemoglobin manifests clinically.
  • If left untreated, sickle-cell disease can result in death.
  • Early clinical features include painful crises, fatigue, and shortness of breath.
  • Common complications include sepsis, hypoxia, tissue infarction, depression, and death.[9]
  • Prognosis is generally guarded in the United States and poor in developing nations.

Diagnosis

Diagnostic Criteria

  • The diagnosis of sickle cell disease is made when a person has:
  • The characteristic genetic mutation (glutamic acid to valine) in beta-globin
  • Symptoms characteristic of sickle cell disease

Symptoms

  • Sickle cell disease is usually symptomatic.

Symptoms of sickle-cell disease include:

Physical Examination

  • Patients with sickle cell disease usually appear ill during times of acute exacerbation of painful crises. If patients are well controlled on their medications, they can appear clinically well.
  • Physical examination may be remarkable for:

Laboratory Findings

The most important laboratory test for sickle cell anemia is a complete blood count (CBC), specifically hemoglobin and hematocrit. Low hemoglobin (anemia) is due to the intrinsic nature of the disease. A positive peripheral blood smear showing sickle-shaped cells is characteristic of sickle cell disease. High total bilirubin with predominantly indirect bilirubin may suggest hemolysis, since bilirubin is a breakdown production of hemoglobin. High lactate dehydrogenase (LDH) may also be seen if there is hemolysis. High reticulocyte count may be seen if the bone marrow is attempting to compensate for the anemia. Low oxygen content on arterial blood gas (ABG) may be observed.

Imaging Findings

  • In some cases, plain imaging such as x ray can be useful, which may reveal subacute or chronic infarcts of the extremities or deformities.
  • CT scan is useful for patients with suspected stroke due to vaso-occlusion.
  • MRI can show avascular necrosis of the leg. It can also show osteomyelitis and marrow hyperplasia.

Other Diagnostic Studies

  • Sickle cell disease does not require any additional diagnostic tests. Newborn screening accurately identifies patients with sickle cell disease.

Treatment

Medical Therapy

  • The mainstay of therapy for sickle cell disease is supportive care. Supportive care includes pain control, transfusions, antibiotics if there is infection, hydration, and oxygenation.

Specific therapies include hydroxyuea, which increases fetal hemoglobin production, exchange transfusions, and stem cell transplant.

Surgery

  • Surgery has no significant role in sickle cell disease.

Prevention

  • There are no primary preventive measures available for sickle cell disease. However, genetic counseling is an option.

Hydroxyurea can prevent sickle cell crises by increasing fetal hemoglobin. Fetal hemoglobin protects against complications of anemia.[10][11]

References

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  2. 2.0 2.1 Forget BG, Bunn HF (2013). "Classification of the disorders of hemoglobin". Cold Spring Harb Perspect Med. 3 (2): a011684. doi:10.1101/cshperspect.a011684. PMC 3552344. PMID 23378597.
  3. Ballas SK, Kesen MR, Goldberg MF, Lutty GA, Dampier C, Osunkwo I; et al. (2012). "Beyond the definitions of the phenotypic complications of sickle cell disease: an update on management". ScientificWorldJournal. 2012: 949535. doi:10.1100/2012/949535. PMC 3415156. PMID 22924029.
  4. Alapan Y, Kim C, Adhikari A, Gray KE, Gurkan-Cavusoglu E, Little JA; et al. (2016). "Sickle cell disease biochip: a functional red blood cell adhesion assay for monitoring sickle cell disease". Transl Res. 173: 74–91.e8. doi:10.1016/j.trsl.2016.03.008. PMC 4959913. PMID 27063958.
  5. Hernigou P, Daltro G, Flouzat-Lachaniette CH, Roussignol X, Poignard A (2010). "Septic arthritis in adults with sickle cell disease often is associated with osteomyelitis or osteonecrosis". Clin Orthop Relat Res. 468 (6): 1676–81. doi:10.1007/s11999-009-1149-3. PMC 2865595. PMID 19885711.
  6. Sankaran VG, Weiss MJ (2015). "Anemia: progress in molecular mechanisms and therapies". Nat Med. 21 (3): 221–30. doi:10.1038/nm.3814. PMC 4452951. PMID 25742458.
  7. Makani J, Ofori-Acquah SF, Nnodu O, Wonkam A, Ohene-Frempong K (2013). "Sickle cell disease: new opportunities and challenges in Africa". ScientificWorldJournal. 2013: 193252. doi:10.1155/2013/193252. PMC 3988892. PMID 25143960.
  8. Brandow AM, Liem R (2011). ""Sickle Cell Disease in the Emergency Department: Atypical Complications and Management"". Clin Pediatr Emerg Med. 12 (3): 202–212. doi:10.1016/j.cpem.2011.07.003. PMC 3172721. PMID 21927581.
  9. Hasan SP, Hashmi S, Alhassen M, Lawson W, Castro O (2003). "Depression in sickle cell disease". J Natl Med Assoc. 95 (7): 533–7. PMC 2594635. PMID 12911250.
  10. Ngo D, Bae H, Steinberg MH, Sebastiani P, Solovieff N, Baldwin CT; et al. (2013). "Fetal hemoglobin in sickle cell anemia: genetic studies of the Arab-Indian haplotype". Blood Cells Mol Dis. 51 (1): 22–6. doi:10.1016/j.bcmd.2012.12.005. PMC 3647015. PMID 23465615.
  11. Fitzhugh CD, Hsieh MM, Allen D, Coles WA, Seamon C, Ring M; et al. (2015). "Hydroxyurea-Increased Fetal Hemoglobin Is Associated with Less Organ Damage and Longer Survival in Adults with Sickle Cell Anemia". PLoS One. 10 (11): e0141706. doi:10.1371/journal.pone.0141706. PMC 4648496. PMID 26576059.