Clinic Notes: Darwin and Autism

Autism is considered to be a genetic disorder by many and numerous researchers are looking for the "autism gene." The concordance rate for autism (the probability for getting autism) is 60% for identical twins, but drops to between 4-8% for fraternal twins and non-twin siblings. In most cases, the number of individuals with a genetic disorder remains constant in within a population unless an individual with the disorder breeds. In the past ten years there has been an explosion in the number of children diagnosed with autism. If autism is a genetic disorder, then why the dramatic increase? Is it evolving in the population? That would not make sense. Natural selection couldn't be operating here and mutations are unlikely with such an explosion of cases. I wonder if epigenetic markers could be a factor. Epigenetic markers sit on genes and tell them to switch on and off. Stress, diet, etc can cause epigenetic marks can switch genes on and off and affect what is passed on the offspring. So if this idea is correct, and I admit this is a long shot, what happened to the parents of the children with autism that perhaps affected the wiring of their brains? Please email me with your hypotheses.