Another view of these disorders is that they are on a continuum known as autistic spectrum disorders. A related continuum is Sensory Integration Dysfunction, which is about how well we integrate the information we receive from our senses. Autism, Asperger's syndrome, and Sensory Integration Dysfunction are all closely related and overlap.
There are two main manifestations of classical autism, regressive autism and early infantile autism. Early infantile autism is present at birth while regressive autism begins before the age of 3 and often around 18 months. Although this causes some controversy over when the neurological differences involved in autism truly begin, some believe that it is only a matter of when an environmental toxin triggers the disorder. This triggering could occur during gestation due to a toxin that enters the mother's body and is transferred to the fetus. The triggering could also occur after birth during the crucial early nervous system development of the child due to a toxin directly entering the child's body.