The reason for the rapid increase in this disabling condition is not clear despite many currently existing theories about causation. There is little doubt however that these represent a complex multi-system disorder group affecting not only the neurological development of a child, but also the gastrointestinal system and immune system in many cases. In identical twin studies, there is a concordance rate of 60-80%, while fraternal twins only show 0-10% concordance and siblings 3-5% concordance. This has led to a tremendous effort in trying to locate a gene or group of genes that result in autism, but no single focus appears to exist. Various chromosomes that have been implicated include chromosome 7q22-33, chromosome 2q, chromosome 15q11-13, chromosome 6q, chromosome 17, and the sex chromosomes. It is most likely that a group of chromosomal abnormalities may exist that predispose a child to some vulnerability in the prenatal or postnatal period. More than 15 different genes have been suspected in resulting in a risk for autism based on genetic linkage studies.

As a result of the fact that identical twins do not share 100% risk, and also that their expression of the disorder when present is so varied, it is supported that environmental contributors are also a major etiologic factor. Likewise, the incredible increase in the last 20 years in prevalence and suspected incidence would also support an environmental agent at play. While a more educated public and medical community may account for an increase in diagnosis and recognition, this would be unlikely to yield such a dramatic increase in such a short time period. There are many suspected agents, and these range from live viruses in vaccines, to mercury preservatives, to poorly metabolized toxic proteins, to yeast, to other yet to be defined environmental toxins. Whether these agents are present in the mother prior to pregnancy, during pregnancy, or in the child early in life is still a mystery. These potential etiologies as well as their related therapies will be discussed.

In regards to what is affected in these disorders, it appears the components of the brain that regulate emotion, communication and social interaction are most affected. These areas are collectively known as the limbic areas of the brain. Functional MRI studies and SPECT studies of the brain, that look at blood flow and metabolism, demonstrate that the most profound changes  occur in the amygdala, hippocampus, insula, pre-frontal area, temporal lobes and cerebellum. Likewise, neuron-pathology examinations of brains of affected individuals support these findings as well. These areas essentially are integral parts of our ability to recognize faces, interact socially, process emotions, communicate, pay attention and perform coordinated motor activities. Whatever the process, it results in multi-focal areas of involvement of the brain that result in the defined complex symptoms of Autism.