• There may be different genes or different combinations of genes involved in causing the different PDDs. Some genes may be found to be associated with more than one disorder. For example, changes in the MECP2 gene have been shown to be associated with Rett disorder, and recently changes in this gene have been found in some individuals with autistic disorder as well.

Asperger Disorder
Individuals with Asperger disorder do not have a delay in spoken language development, but can have serious deficits in social and communication skills.

Pervasive Developmental Disorder Not Otherwise Specified (PDD/NOS)
Is a diagnosis often considered for children who show some signs of autistic disorder, but who do not meet the specific diagnostic criteria for the other PDDs.

Rett Disorder
Rett disorder is among the most common genetic cause of profound intellectual and physical disability in girls, occurring more commonly than 1 in 10,000 female births.

Childhood Disintegrative Disorder
Children with childhood disintegrative disorder develop normally for a relatively prolonged period before developing a condition that resembles autistic disorder.