The occurrence of developmental regression in autism is one of the most puzzling features of these pervasive developmental disorders. It is well known that in some cases of so-called regressive autism deterioration of communicative, cognitive and social functions usually occurs in the second year of life, after period of normal postnatal development. Although natural developmental trajectory of autistic disorder is characterized by continual increase in communication and social abilities, more than 20% of the adolescents with autism experience marked deterioration, possibly due to the seizures or comorbid psychiatric disorders. However, in the majority of the cases it is still not known why the regression occurs. In the future research one ...