Rett syndrome: An X-linked dominant neurological disorder that affects girls only and is one of the most common causes of mental retardation in females. Girls with the syndrome show normal development during the first 6-18 months of life followed first by a period of stagnation and then by rapid regression in motor and language skills. The hallmark of Rett syndrome is the loss of purposeful hand use and its replacement with stereotyped hand-wringing. Screaming fits and inconsolable crying are common.
Other key features include loss of speech, behavior reminiscent of autism, panic-like attacks, bruxism (grinding of teeth), rigid gait, tremors, intermittent hyperventilation, and microcephaly (small head). Seizures occur in about half of cases. The girls typically survive into adulthood, but are at risk of sudden unexplained death. Rett syndrome is due to mutation in the MECP2 gene (methyl-CpG-binding protein-2) on chromosome Xq28. The vast majority of cases are sporadic and result from a new mutation in the girl with Rett syndrome or inheritance of the mutation from a parent who has somatic or germline mosaicism with the MECP2 mutation in only some of their cells. Atypical Rett syndrome with MECP2 mutations has been found in patients previously diagnosed with autism, mild learning disability, and mental retardation with spasticity or tremor. Males with a MECP2 mutation suffer severe encephalopathy (brain disease) and die before their first birthday.
After normal development up to the age of 6 to 18 months, developmental stagnation occurs followed by rapid deterioration of high brain functions. Within 1 to 2 years, this deterioration progresses to loss of speech, severe dementia, behavior reminiscent of autism, stereotypic hand-wringing movements, loss of purposeful use of the hands, jerky ataxia (wobbliness) of the trunk, intermittent hyperventilation, and microcephaly (small head).
Thereafter, a period of apparent stability lasts for decades. But additional neurologic abnormalities intervene insidiously These abnormalities include what is called spastic paraparesis (paralysis and spasticity of the legs) and epilepsy (seizures). A striking deceleration of growth has been found across all measurements in most girls with Rett syndrome who end up with short stature and microcephaly.
The mortality (death) rate among children with Rett syndrome is increased (1.2% per year). A high proportion (26%) of the deaths are sudden and associated with a heart conduction problem, namely an abnormally prolonged QT interval on the electrocardiogram.
The syndrome that bears his name was first described by Andreas Rett, an Austrian pediatrician, in 1966. The frequency of Rett syndrome -- about 1 in 10-20,000 girls -- appears similar in southwest Sweden, North Dakota, and metropolitan Tokyo.