PDD comprises a wide range of delays of different magnitude in different areas.
Autism is the most severe of the pervasive developmental disorders.
These individuals can exhibit a variety of characteristics, and the disorder can range from mild to severe. In contrast to Autism, there are no clinically significant delays in language or cognition or self help skills or in adaptive behavior, other than social interaction. The child with RS usually shows apparently normal or near normal development until 6-18 months of life. A period of temporary stagnation or regression follows during which the child loses communication skills and social withdrawal . These children have seemingly normal development for at least the first 2 years after birth.