Autism spectrum disorder is a term used to describe several developmental disabilities. Such conditions include autism, Asperger syndrome, childhood disintegrative disorder, Rett syndrome and pervasive developmental disorder. The latter is used to describe atypical cases of autism and is believed to be the most common Autism Spectrum Disorders. Symptoms of these conditions tend to surface during the first two years of life and are usually diagnosed at around three to four years of age.

Autism is the most well known disorder of the autistic spectrum. The most dominant symptoms of autism are extreme difficulty with social interactions and communication, both verbal and non-verbal. Children with autism also may participate in repetitive behavior such as flapping of the hands or head rolling. Severity of the symptoms vary greatly, and with proper therapy and medication a child who lives with a high functioning type of autism can integrate seamlessly into society.

Asperger syndrome is also characterized by difficulty with social interaction and communication, however there is generally no delay in the acquisition of language skills. People with Asperger's often have a large vocabulary at an early age and may be of above average intelligence. However it is often difficult for them to make friends and maintain relationships, as they are often perceived as having a lack of empathy, or even being downright rude. Cognitive Behavioral Therapy can be very helpful in teaching someone afflicted with Asperger syndrome how to function properly in social situations.

Childhood disintergrative disorder is different in that it's symptoms usually does not begin to appear until after three years of age. After developing normally the child in question rapidly regresses, losing language, social function and motor skills. This disorder is rare and is considered a low functioning autistic spectrum disorder.

Rett Syndrome is also known as “cerebroatrophic hyperammonamea”. It effects mostly females and the symptoms can be quite severe. Physical symptoms such as small hands and feet are often present, and about half of the individuals who suffer from Rett syndrome can not walk. People with Rett syndrome usually have no verbal skills and also suffer from other problems such as gastrointestinal disorders.

Pervasive Developmental Disorder-not otherwise specified or PDD-NOS, is a term used for conditions in which the subject exhibits difficulty in social development and communication but does not meet enough criteria to warrant a diagnosis of one of the other autism spectrum disorders. People who are classified in this manner generally experience milder symptoms than with the other disorders, with the exception of Asperger syndrome. The symptoms of Asperger's large overlap of PDD-NOS, the key difference being that in cases of Asperger syndrome there is generally no speech delay.

The five disorders on the Autism spectrum have varying degrees of severity and prognosis. They can also be difficult to diagnoseose due to a high degree of commorbity with other disorders such as learning disabilities or epilepsy.

Regardless of the condition proper therapy and medication is imperative in ensuring that anyone suffering from these conditions receives the highest quality of life possible.