Why would there be a huge increase in autism and retardation in the population?

Don't know: To be clear, there is no increase in retardation; in fact, if anything, mr as a diagnosis has nearly disappeared, as many of these individuals now are called autistic. Why autism and related disorders has become so much more common remains an area of intense study. Part of it was a broadening of the criteria, so many more were included; but, many argue that other factors are at play.

Multifactorial: Because the presentation of autism spectrum disorders is so varied and the incidence is increasing significantly the effect of environmental factors on genetics is proving to play a big role. They are many subtle ways the environment can afffect the expression of certain genes and we are learning of new genetic variants constantly. Protect your environment to protect your genes.

Genetic & epigenetic: Factors (that alter function but not structure or sequence of fetal genes) can cause the set-up for autistic spectrum disorder. Though atypical white matter changes on brain mri's & ⬇ed eye-to-face gaze are found in 6-mo.-olds, overt clinical symptoms may present 12-18 mos. Later. Daily Folic Acid supplements & flu vaccine at least 3 mos. Prior to conception ⬇ the risk of having a child with asd.