Presently, there is no medical test to determine whether a person has autism, and the diagnosis is indicated when an individual displays certain characteristic behaviors as defined by the Diagnostic and Statistic Manual, Fourth Edition. The daily functioning level of Autistic people varies to such a large extent that the disorder has recently been renamed Autistic Spectrum Disorder. It is a disorder of the Nervous System and of the immune system that affects multiple metabolic pathways. It is possible that autism may be the result of a G-alpha protein disruption, which affects the retinoid receptors which modulate sensory input. Autism is four times more prevalent in males than in females.
Tuberous sclerosis is currently the second largest identifiable genetic cause of autism.
A genetic component coupled with infant exposure to mercury may also contribute to the development of autism. Thimerosal, which contains mercury is an additive in vaccines used to prevent bacterial and fungal contamination. Recently, a neurologist hypothesized that autism may be categorized into two distinct forms. The first form is an idiopathic autism, resulting from a familial connection. Under this subgroup, some autistic individuals also have other genetic disorders, such as Fragile X Syndrome, Landau- Kleffner Syndrome, William's Syndrome, or Tourette's Syndrome.