Autism / Autism Spectrum Disorder (ASD) (also Pervasive Developmental Disorder-PDD) is considered to be a biological disorder of brain development, not an emotional disorder and affects social development, communication and behaviour. Associated symptoms may include seizure disorders, marked sensory disturbances, and motor abnormalities.

It is still not known what causes this abnormal brain development, as there is no reliable information obtained through brain scans and other medical tests. Current research suggests the possibility of multiple causes which may include a physical problem affecting areas of the brain that process language and information coming in from the senses; an imbalance of certain chemicals in the brain; genetic factors and viral infections. Autism may coexist with other disabilities (Autism Society NB). Certain known causes of Autism/ASD are PKU and congenital Rubella.

Better understanding over the past few years has resulted in earlier and improved identification and treatment. Autism is considered to be a part of a spectrum disorder that varies in severity and etiology. It is now referred to many times as Autism Spectrum Disorder (ASD) or Pervasive Developmental Disorder (PDD), although these are merely umbrella terms of which Autism is a subtype. PDD also includes Rhett's Syndrome, Childhood Disintegrative Disorder, PDD Not Otherwise Specified (PDD-NOS), and Asperger's Syndrome, which is a less severe form but shares the same core features; impairments in social interaction and communication, and a tendency towards repetative, ritualized behaviour.

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