There are five pervasive developmental disorders. Each disorder is considered a spectrum disorder so the severity of the symptoms ranges from mild to severe. Each of the pervasive developmental disorders is defined by the DSM IV. PDD-NOS is pervasive developmental disorder-not otherwise specified. This diagnosis covers all cases that involve individuals who show some symptoms of PDD but who fail to fall into one specific category. The diagnosis of PDD-NOS also involves unusual cases as well. Autism is the most recognized of the pervasive developmental disorders and it involves a combination of social, communication and behavioral problems that interfere with the individual's ability to navigate through everyday situations. Autistic disorder ranges in severity from very mild to profound. Asperger's syndrome is unique among the pervasive developmental disorders because these individuals do not show deficits in language acquisition. The social impairments are apparent in Asperger's disorder and these individuals exhibit stereotyped, repetitive movements as well as a need for order. Rett's disorder is commonly found in females. Males who have the disorder do not survive long past birth. Individuals who have Rhett's disorder develop normally until the ages between five and 24 months of age. The child loses skills including hand coordination and language skills and continues to regress from there. Childhood disintegrative disorder appears between two and 10 years of age. The child suddenly loses social, communication and motor skills with little or no warning. Childhood disintegrative disorder is the rarest of the five PDDs.