I don't understand why, as people, we are so willing to accept a zany explanation when perfectly good scientific explanations are available - and have been available for many years. On the top of my frustration list right now is autism. Back in 1995 (nearly 15 years ago), it was identified that there is a very strong genetic component to developing autism and autism spectrum disorders. From this paper by Bailey and colleagues:
SYNOPSIS Two previous epidemiological studies of autistic twins suggested that autism was predominantly genetically determined, although the findings with regard to a broader phenotype of cognitive, and possibly social, abnormalities were contradictory.Obstetric and perinatal hazards were also invoked as environmentally determined aetiological factors. The first British twin sample has been re-examined and a second total population sample of autistic twins recruited. In the combined sample 60% of monozygotic (MZ) pairs were concordant for autism versus no dizygotic (DZ) pairs; 92% of MZ pairs were concordant for a broader spectrum of related cognitive or social abnormalities versus 10% of DZ pairs. The findings indicate that autism is under a high degree of genetic control and suggest the involvement of multiple genetic loci. Obstetric hazards usually appear to be consequences of genetically influenced abnormal development, rather than independent aetiological factors. Few new cases had possible medical aetiologies, refuting claims that recognized disorders are common aetiological influences.
Furthermore, although we know that autism is highly heritable, it is not the product of a single gene - which is likely why we observe a spectrum of autism-like affects. And, no matter how often mindless drones like to repeat it, over 200 studies show that there is absolutely no link between autism and thimerosol-containing vaccinations.
There is still much debate as to whether there is an autism epidemic, or whether our definition and diagnosis of autism spectrum disorders has increased. For example, both because of stigma, and because of the lack of a formal definition, clinical depression is not identified in many cultures.