Almost all of the researchers in this field of study agree that genetic predisposition is crucial in the neurological foundation of autism. It has been shown that if one of a pair of identical twins is autistic, there is a 90 percent chance the other twin will be autistic. Furthermore, parents of one autistic child who’s risk is 1 in 500 of having an autistic child, rises to 1 in 20 with a second child. After two autistic children, this risk increases to 1 in 3. In addition, "the chances that the siblings of an autistic child will display one or more of the other developmental disorders with a known genetic basis – such as dyslexia or Tourette’s syndrome – are also significantly higher than normal."
One most curious aspect is the dramatically higher incidence of this in Silicon Valley and the Route 128 area outside of Boston. Some high functioning people who work in these areas are considered "broad autistic phenotypes". "One provocative hypothesis that might account for the rise of spectrum disorders in technically adept communities like Silicon Valley, some geneticists speculate, is an increase in assortative mating."
This phenomena is not occurring in just the previously mentioned areas, but also in other places where a concentration of technically advanced people are having children, as well as an increase of reported rates all over the world. There is cause for alarm and an urgent need to mobilize research efforts.
The most detailed medical analysis of autism by far can be found in Topics in Clinical Chiropractic. The most detailed social analysis is in Wired magazine. The most instructive is Behavioral Intervention for Young Children with Autism. There are other sources full of valuable information on the topic. Space prohibits their inclusion and discussion at this time.
Autism remains a puzzle. It is generally believed to be a genetic disorder related to a variant allele of HOXB1, a gene on chromosome 17, possibly regions on chromosome 15, chromosome 7 and chromosome 9. A remarkable and detailed report on the etiologies, brain mechanisms, and neuropsychological phenotypes can be found in Diagnosing Learning Disorders; A Neuropsychological Framework (which may be now outdated). This following description is a valuable bit of information from this 1991 book:
…Briefly, existing evidence supports the conclusion that autism is familial, heritable and genetically heterogeneous. Among the possible genetic subtypes are multifactorial inheritance, autosomal recessive inheritance, X-linked inheritance and nonfamilial chromosomal anomalies.
Here are some sources...
Silberman, Steve. "The Geek Syndrome." Wired Dec 2001: 176.
Brian J Gleberzon and Anita L Rosenberg-Gleberzon. "On autism: Its prevalence, diagnosis, causes, and treatment." Topics in Clinical Chiropractic. Dec 2001.
http://proquest.umi.compdqweb?TS=1019705267&RQT=309&CC=2&Dtp=1&Did>
Maurice, Catherine, ed. Behavioral Intervention for Young Children with Autism. Austin: PRO-ED, 1996.
Rodier, Patricia M. "The Early origins of Autism." Scientific American. Feb 2000: 56.
Bower, B. "Gene Implicated in Development of Autism." Science News. Dec 16, 2000: 390.
Holden, Constance. "The Destiny of Autism?" Science Now. Dec 6, 2000: 3.
Pennington, Bruce F. Diagnosing Learning Disorders; A Neuropsychological Framework. New York: Guilford Press, 1991.