Due to the broad range of forms in which it can exist, autism is considered one of a group of spectrum disorders. Autism is the most common of the five Pervasive Development Disorders (PDD). These include Autistic Disorder, Asperger’s Disorder, Childhood Disintegrative Disorder, Rett’s Disorder, and Pervasive Development Disorders -Not Otherwise Specified (PDD-NOS). These are all neurological disorders characterized by “severe and pervasive impairment in several areas of development,” including social interaction and communication skills. Though they all may have some of the same symptoms, but they differ in terms of when the symptoms start, how fast they appear, how severe they are, and their exact nature
There is currently no known cause for Autism Spectrum Disorders. What we do know is that autism spectrum disorders are multifaceted communication and sensory impairments that impede the processing of information. The spectrum makes the diagnosis of autism extremely difficult. Autism is frequently missed, or sometimes misdiagnosed as something else. Although symptoms are almost always present before age 3, autism is often not diagnosed until 2-3 years of age.
Although there is no known cure for autism, it is important to remember that autism spectrum disorders are treatable. Early and intensive treatment can help children with autism improve their communication and social skills. The Living With Autism Program focuses on recognizing the individual needs of children and families affected by autism. Individualized treatment plans are designed and reevaluated regularly to emphasize development of communication skills, neutralization of behavior problems and participation in natural social exchanges and environments.

Asperger’s Syndrome
Asperger's Syndrome, also known as Asperger's Disorder or Autistic Psychopathy, is a Pervasive Developmental Disorder (PDD) characterized by severe and sustained impairment in social interaction, development of restricted and repetitive patterns of behavior, interests, and activities. Asperger's Disorder appears to have a somewhat later onset than Autistic Disorder, or at least to be recognized somewhat later. In Asperger's Disorder, affected individuals are characterized by social isolation and eccentric behavior in childhood. There are impairments in two-sided social interaction and non-verbal communication. However, social and communication deficits are less severe. In contrast to Autistic disorder (Autism), there are no clinically significant delays in language or cognition or self-help skills or in adaptive behavior, other than social interaction.

Rett Syndrome
Rett Syndrome is a neurological disorder seen almost exclusively in females, and found in a variety of racial and ethnic groups worldwide. The child with Rett Syndrome usually shows an early period of apparently normal or near normal development until 6-18 months of life. Gradually, mental and physical symptoms appear. Hypotonia (loss of muscle tone) is usually the first symptom. Other early symptoms may include problems crawling or walking and diminished eye contact. A period of temporary stagnation or regression follows during which the child loses communication skills and purposeful use of the hands. Soon, stereotyped hand movements, gait disturbances, and slowing of the rate of head growth become apparent. The loss of functional use of the hands is followed by compulsive hand movements such as wringing and washing. Rett Syndrome is believed to affect 1 in 10,000 females

Childhood Disintegrative Disorder
There are well documented cases where children develop normally up to the age of three and then demonstrate a regression in either social or language skills or both. This regression may be precipitated by a clear neurological event such as epilepsy or meningitis or can be associated with a vague flu-like illness. It is not uncommon, however, that the regression is not associated with a clear cut precipitant. Children who meet the criteria for Childhood Disintegrative Disorder exhibit the social and communicative deficits and behavioral features generally associated with Autistic Disorder.

Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS)
A diagnosis of PDD-NOS is typically made when there is significant and pervasive impairment in the development of reciprocal social interaction, poor verbal or nonverbal communication, and presence of stereotypical behaviors, interests, or activities, but the criteria are not met for a specific Pervasive Developmental Disorder.