Pervasive Developmental DisorderThe category of pervasive developmental disorders (PDD) includes autistic disorder, Rett syndrome, Childhood disintegrative disorder (CDD), Asperger’s disorder, and pervasive developmental disorder–not otherwise specified (PDDNOS; American Psychiatric Association [APA], ). PDD is characterized by impairment during the first few years of life in social, affective, communicative, and cognitive development. It is difficult to estimate an overall prevalence rate for the five disorders due to disagreement regarding different diagnosis. For example, there is some research to suggest that autism and PDDNOS are different points on a continuum (Tsai,).
Prevalence rates for disorders in the PDD category are as follows: Autism and Aspergers together occur in 1 per 1,000 children, Rett syndrome occurs in approximately 1 in 10,000–15,000 (primarily females), and CDD is extremely rare (Tanguay,). The increasing incidence of PDD disorders is due in part to greater knowledge regarding diagnosis and broader diagnostic categories. Social class was thought to affect the occurrence of PDD; however, research indicates that PDD occurs across all social classes (Klinger & Dawson,). PDD is 3 to 4 times greater in males than in females and is found all over the world, with similar incidence and prevalence rates regarding gender, social class, and cognitive abilities. Rett syndrome is primarily found in females; few male cases have been documented. Differential diagnosis is needed for disorders within the PDD category as well as several other disorders, including developmental language delay, childhood schizophrenia, a degenerative central nervous system disorder, and Landau-Kleffner syndrome.