While it was not understood as a spectrum disorder like it is today, it is pretty clear that there has been a relatively low basal rate of autism in all societies in at least the last few thousand years. Autism is a normal risk of being born human, and in all likelihood, being born a higher mammal, as autistic behaviors have been demonstrated in many species of mammals. An obvious question is what causes autism, or at least autistic behaviors, to have been present at low levels in the human past.

A. Specific Genetic and Environmental Causes of Autism

About 10-15% of autism cases appear to be caused by single factor genetic abnormalities or environmental exposures. However, many people don’t view these conditions involving autism, instead involving autistic like conditions, since the causation behind autism is supposed to be a mystery. And, the incidence of autism as a result of these single vector abnormalities does not appear to be increasing dramatically like the incidence of idiopathic autism – therefore, autism in which the cause can be identified is differentiated from classic autism for which no cause has been determined.

     1. Genetic Causes

Somewhere between 5% and 15% of autism cases are caused by a chromosomal abnormality in the human genome that results in various symptoms in the child suffering from this genetic defect, including a greatly increased risk of developing autism. Chromosomal abnormalities that result in frequent autism diagnoses are involved in a wide variety of conditions including Fragile X Syndrome, Rett Syndrome, Tuberous Sclerosis, Prader Will Syndrome, Angelman Syndrome, Down Syndrome, Smith-Lemli-Opitz syndrome (“SLOS”), Phenylketonuria, Cornelia de Lange Syndrome, and Lactic Acidosis. The rate of diagnosis of autism in these populations varies widely, probably from 5% to 80% of cases...

To read more, click on the Download to the left.