Background Information
Rett syndrome is a severe progressive neurological condition that develops in early childhood and affects only girls. Andreas Rett first described Rett syndrome in 1966, but recognition of the syndrome outside Europe did not occur until the early 1980s. With an estimated incidence of 1 in 10,000, Rett syndrome is the second most common cause (after Down syndrome) of mental retardation in females.
Girls with Rett syndrome have normal growth and development during the first few months of life. The clinical features begin to develop between 6 months and 3 years of life. Over a period of months to years there is a progressive loss of previously acquired motor skills, regression in language and communication skills and the onset of stereotypical hand movements. The clinical course for girls with classical Rett Syndrome is a progression through several stages of global neurologic decline accompanied by poor head growth and growth failure. Ultimately girls affected with this condition become totally dependent and the majority will die in late adolescence or early adulthood.
The diagnosis of Rett syndrome is made according to a set of diagnostic criteria, but several clinical variants have been described and there is clinical overlap with other neuro-developmental conditions such as Angelman syndrome.
MeCP2
mutations have been found in ~5% of atypical Angelman syndrome cases. In addition there are many cases of developmental regression in girls where, after extensive investigation, no definitive diagnosis is made. Since the
MeCP2
gene is involved in a very fundamental biologic process it is possible that some girls with unexplained developmental regression may have mutations in this gene. More recently there have been other cases where
MeCP2
mutations have been found, including some X-linked mental retardation pedigrees where there are retarded males with mutations in the gene.
About 75% of girls with Rett syndrome have mutations in
MeCP2
. Some rare pedigrees have affected girls and cases of males with a severe neonatal severe encephalopathy. These boys have also had
MeCP2
mutations confirming the X-linked dominant genetics, and demonstrating unique sex-limited disease phenotypes.
