About PDD (NOS) Autism and Pervasive Developmental Disorder-NOS (not otherwise specified) are developmental disabilities that share many of the same characteristics. Usually evident by age three, autism and PDD-NOS are neurological disorders that affect a child’s ability to communicate, understand language, play, and relate to others. Due to the similarity of behaviors associated with autism and PDD, use of the term pervasive developmental disorder has caused some confusion among parents and professionals. However, the treatment and educational needs are similar for both diagnoses. Autism and PDD occur in approximately 5 to 15 per 10,000 births. These disorders are four times more common in boys than girls. The causes of autism and PDD are unknown. Currently, researchers are investigating areas such as neurological damage and biochemical imbalance in the brain. These disorders are not caused by psychological factors. Some or all of the following characteristics may be observed in mild to severe forms: Communication problems (e.g., using and understanding language); Difficulty in relating to people, objects, and events; Unusual play with toys and other objects; Difficulty with changes in routine or familiar surroundings; and Repetitive body movements or behavior patterns. Children with autism or PDD vary widely in abilities, intelligence, and behaviors. Some children do not speak; others have limited language that often includes repeated phrases or conversations. People with more advanced language skills tend to use a small range of topics and have difficulty with abstract concepts. Repetitive play skills, a limited range of interests, and impaired social skills are generally evident as well. Unusual responses to sensory information -- for example, loud noises, lights, certain textures of food or fabrics -- are also common. Information on this page is thanks to  Feralcheryl5