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Rett syndrome (also called Retts disorder) is a neurodevelopmental disorder that is classified as a pervasive developmental disorder by the DSM-IV. It was first described by Austrian neurologist Andreas Rett in 1966. The clinical features include a deceleration of the rate of head growth (including microcephaly in some) and small hands and feet. Stereotypic, repetitive hand movements such as mouthing or wringing are also noted. Symptoms of the disorder include cognitive impairment and problems with socialization, the latter during the regression period. Socialization typically improves by the time they enter school. Girls with Rett syndrome are prone to gastrointestinal disorders and up to 80% have seizures.[1] They typically have no verbal skills, and about 50% of females are not ambulatory. Scoliosis, growth failure, and constipation are very common and can be problematic. Many argue that it is misclassified as a pervasive developmental disorder, just as it would be to include such disorders as fragile X syndrome, tuberous sclerosis, or Down syndrome where one can see autistic features.[2] The symptoms of this disorder are most easily confused with those of Angelman syndrome, cerebral palsy and autism.
Rett syndrome (symbolized RTT) is caused by mutations in the gene MECP2 located on the X chromosome and can arise (1) sporadically or (2) from germline mutations.
Rett syndrome is usually caused (95% or more) by a de novo mutation in the child (so it is NOT inherited from either parent. Parents are generally genotypically normal, i.e. one without a MECP2 mutation).
In sporadic cases of Rett syndrome, it is thought that the mutated MECP2 is usually derived from the male copy of the X chromosome. [3]It is not yet known what causes the sperm to mutate, and such mutations are rare.
It can also be inherited from phenotypically normal mothers who have a germline mutation in the gene encoding methyl-CpG-binding protein-2, MECP2.[4] MECP2 is found near the end of the long arm of the X chromosome at Xq28. An atypical form of Rett syndrome, characterized by infantile spasms or early onset epilepsy, can also be caused by a mutation to the gene encoding cyclin-dependent kinase-like 5 (CDKL5). Rett syndrome affects one in every 12,500 female live births by age 12 years.
It almost exclusively affects girls — male fetuses with the disorder rarely survive to term. Development is typically normal until 6-18 months, when language and motor milestones regress, purposeful hand use is lost and acquired deceleration in the rate of head growth (resulting in microcephaly in some) is seen. Hand stereotypies are typical and breathing irregularities such as hyperventilation, breathholding, or sighing are seen in many. Early on, autistic-like behavior may be seen.
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