It is also called as Cerebroatrophic hyperammonemia . A rare genetic postnatal neurological disorder of the grey matter of the brain that almost exclusively affects females.
• Deterioration over several months of intellectual, social, and language function
• Occur in 3- and 4-year-olds with previously normal functions.
• Closely resemble children with autistic disorder.
Asperger's disorder is characterized by impairment in social interaction and restricted interest without any delay in language, cognitive development, or age-appropriate self-help skills.
Childhood disintegrative disorder
Childhood disintegrative disorder is characterized by marked regression in several areas of functioning after at least 2 years of apparently normal development.
Childhood disintegrative disorder, also called Heller's syndrome and disintegrative psychosis
Further suggested reading - WEBMD