Angelman syndrome: A neurodevelopmental disorder characterized by severe motor and intellectual retardation, ataxia, frequent jerky limb movements and flapping of the arms and hands, hypotonia, seizures, absence of speech, frequent smiling and episodes of paroxysmal laughter, open-mouthed expression revealing the tongue.
Mental retardation, X-linked, syndromic, 13: A disorder characterized by significantly below average general intellectual functioning associated with impairments in adaptive behavior and manifested during the developmental period. MRXS13 patients manifest mental retardation associated with other variable features such as spasticity, episodes of manic depressive psychosis, increased tone and macroorchidism.
Rett syndrome: An X-linked dominant neurodevelopmental disorder, and one of the most common causes of mental retardation in females. Patients appear to develop normally until 6 to 18 months of age, then gradually lose speech and purposeful hand movements, and develop microcephaly, seizures, autism, ataxia, mental retardation and stereotypic hand movements. After initial regression, the condition stabilizes and patients usually survive into adulthood.
Autism, X-linked 3: A complex multifactorial, pervasive developmental disorder characterized by impairments in reciprocal social interaction and communication, restricted and stereotyped patterns of interests and activities, and the presence of developmental abnormalities by 3 years of age. Most individuals with autism also manifest moderate mental retardation.
Encephalopathy, neonatal severe, due to MECP2 mutations: A neurodevelopmental disorder characterized by severe neonatal encephalopathy, developmental delay, mental retardation, microcephaly, seizures. Additional features include respiratory insufficiency and central hypoventilation, gastroesophageal reflux, axial hypotonia, hyperreflexia and dyskinetic movements.
Mental retardation, X-linked, syndromic, Lubs type: A disorder characterized by significantly below average general intellectual functioning associated with impairments in adaptive behavior and manifested during the developmental period. MRXSL patients manifest mental retardation associated with variable features. They include swallowing dysfunction and gastroesophageal reflux with secondary recurrent respiratory infections, hypotonia, mild myopathy and characteristic facies such as downslanting palpebral fissures, hypertelorism and a short nose with a low nasal bridge.