As a very insightful reader pointed out a few weeks ago, the discussion of etiology of ASD is all about subsets. Asking "What causes ASD?" is like asking "What causes fever?" The answer, in both cases, is "lots of things."
One way to organize our thinking is to divide up the landscape into "Pure" and "Syndromic" causes of ASD. By "pure" ASD, we mean that there are no physical malformations, and (usually) no Mental Retardation - just ASD. On the other hand, "syndromic" ASD refers to ASD within the context of some larger, identifiable medical disorder, typically associated with physical abnormalities, and/or Mental Retardation. The relative size of these 2 populations is suggested by the sizes of the two parts of the pie graph.
"Syndromic" ASD is made up of a long list of discrete entities, some of which are reasonably common, and some of which are quite rare. I've listed some of these according to the mechanism of causation: Single gene abnormalities, chromosomal abnormalities, exposure to drugs or chemicals during gestation ("teratogenic"), as well as malformations of unknown cause. This list will continue to grow, as specific disorders are teased out from the vast pool of children with ASD. To date, there are no data to establish proof of causation from gluten, or any relationship between yeast in the gut and ASD. We have dealt with the lack of evidence of a causal role for immunizations in earlier posts.
The single biggest factor in "Pure" ASD is family genetics. There are dozens (perhaps more) genes involved, that get shuffled and re-dealt, and passed along from generation to generation within families. In various combinations, these genes can give rise not only to ASD, but to a variety of other autistic-like disorders (Nonverbal Learning Disability, Broad Autistic Phenotype), as well as Non-ASD Neurpsychiatric Disorders, such as Anxiety Disorder, Depression, Bipolar Disorder, Obsessive-Compulsive Disorder, and Alcoholism. When we look at the extended families of children who present with ASD, we discover that the prevalence of all of these conditions is very high. (See my book for literature citations).
Not only do these non-ASD neuropsychiatric disorders run in the families of children on the spectrum; they also lay in wait for children who "outgrow" their diagnosis of ASD (Alas, "losing the diagnosis" of ASD does not equal "cure"). More on this in our next post.
