Turner syndrome overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Akash Daswaney, M.B.B.S[2]
Overview
Historical Perspective
Turner syndrome was first described in 1938 by Henry Turner when he noticed a triad of short stature, cubitus valgus and pterygium colli. Other scientists went to to discover the pathophysiology of the 45 XO karyotype and the presence of streaked ovaries.
Classification
There is no established system for the classification of Turner syndrome.
Pathophysiology
Humans have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. Two of these chromosomes, the sex chromosomes, determine if you become a boy or a girl. Loss the paternally or maternally derived X chromosome would lead to the class 45 XO karyotype. Sometimes, an individual may have two cells lines with different genetic makeups. The percentage of this mosaicism is said to determine the severity of the phenotype in the patient. Structural abnormalities such as the formation of a ring chromosome or an isochromosome and other mechanisms such as lyonization or imprinting also play a role in the pathophysiology of Turner Syndrome.
Causes
Humans have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. Two of these chromosomes, the sex chromosomes, determine if you become a boy or a girl. Females normally have two of the same sex chromosomes, written as XX. Males have an X and a Y chromosome (written as XY). In Turner syndrome, cells are missing all or part of an X chromosome. The condition only occurs in females. Most commonly, the female patient has only one X chromosome. Others may have two X chromosomes, but one of them is incomplete. Sometimes, a female has some cells with two X chromosomes, but other cells have only one.
Differentiating Turner syndrome from Other Diseases
Turner's syndrome must be differentiated from other diseases that cause latency in secondary sexual characteristics development, such as constitutional delay of puberty, hypopituitarism, delayed puberty, and chromosomal abnormalities. Chromosomal abnormality is Noonan's syndrome.
Epidemiology and Demographics
The incidence rate of Turner is 1 of 2500 live births. Turner Syndrome patients have a higher mortality rate compared to the general population.
Risk Factors
There is currently no known cause for Turner syndrome, though there are several theories surrounding the subject.
Screening
Screening for complications of Turner syndrome starts as early as a prenatal visit. Abnormal maternal serum screening tests or an ultrasound detecting structural anomalies such shortned limbs, cystic hygromas, congenital heart defects or increased swelling of the hands or feet may point towards a diagnosis of Turner syndrome. As the years progress, screening involves a multidisciplinary combination of lab investigations (such as serum gonadotrophins,liver function tests, renal function tests, etc), referral to other departments (cardiology, endocrinology, ophthalmology, etc) and tools such as DEXA scans, X-rays, echocardiography, etc.
Natural History, Complications, and Prognosis
Natural history of the patient would depend on the age of the diagnoses and what complications have developed by the time the patients presents to the physician. Congenital lymphedema may take several years to decrease. The patient experiences low self esteem due to their short stature, decreased visual spatial functioning, hyperactivity, poor facial recognition and preference for social isolation. As soon as the patient is capable of understanding, counseling regarding the risks and benefits of Turner syndrome should be explained. When compared to the general population, Turner syndrome patients have an increased mortality rate.
Diagnosis
Diagnostic Study of Choice
The diagnostic study of choice for the diagnosis of Turner syndrome is karyotype analysis of 30 blood lymphocytes. Examination of additional cells , polymerase chain reaction, fluorescent in situ hybridization, Southern blotting, restricted fragment length polymorphisms and new generation gene sequencing techniques may be employed following the interpretation of the initial karyotype.
History and Symptoms
Natural history of the patient would depend on the age of the diagnoses and what complications have developed by the time the patients presents to the physician. Congenital lymphedema may take several years to decrease. The patient experiences low self esteem due to their short stature, decreased visual spatial functioning, hyperactivity, poor facial recognition and preference for social isolation. As soon as the patient is capable of understanding, counseling regaridng the risks and benefits of Turner syndrome should be explained.
Physical Examination
Physical examination may be suggestive of thyroid dysfunction, congenital heart defects, inflammatory bowel disease, characteristic skeletal deformities and body habitus/skin manifestations.
Laboratory Findings
Laboratory investigations serve as important screening tools for thyroid dysfunction, renal dysfunction, liver dysfunction, new onset diabetes mellitus,vitamin D deficiency and ovarian reserve.
Electrocardiogram
An electrocardiogram is not employed in the diagnosis of Turner syndrome.
X-ray
A x-ray may be used to diagnose cardiac and skeletal abnormalities.
Echocardiography and Ultrasound
Prenatal ultrasounds my show a left-sided cardiac defect, renal anomalies, growth retardation, relatively short limbs, fetal edema, cystic hygroma, polyhydramnios and brachycephaly. Echocardiographies and renal ultrasounds help detect structural defects.
CT scan
Simple CTs or CT angiographies are helpful in screening/detecting the following cardiac abnormalities.
MRI
Cardiac MRIs are helpful in screening/detecting the following cardiac abnormalities and functional MRIs have been used to study neural pathways responsible for poor visual spatial skills and executive function.
Other Imaging Findings
There are no other imaging findings associated with Turner syndrome.
Other Diagnostic Studies
The diagnostic study of choice for the diagnosis of Turner syndrome is karyotype analysis of 30 blood lymphocytes. Findings may include the classic 45 XO karyotype, mosaicism and structural anomalies like isochromosomes or ring chromosomes.
Treatment
Medical Therapy
Medical therapies include growth hormone, estrogen replacement therapy, oxandrolone (if growth hormone achieves suboptimal height), vitamin D supplementation, oral hypoglycemic agents and anti-hypertensives.
Interventions
Psycosocial interventions aimed at treating ][visual spatial and executive function]] deficits along with in vitro fertilization (for infertility) are the interventions commonly used in Turner syndrome.
Surgery
Surgery is indicated for craniofacial anomalies, to decrease the risk of aortic dissection and for congenital pterygium colli.
Primary Prevention
There are no established measures for the primary prevention of Turner syndrome.
Secondary Prevention
There are no established measures for the secondary prevention of Turner Syndrome. Secondary prevention is aimed at preventing complications of Turner syndrome. This involves frequent screening of complications.
References