Twin and family studies provide convincing evidence that hereditary factors explain nearly all the etiological variance in the particular populations studied in Britain, Sweden and the US. Unaffected members of discordant MZ twin pairs often have mild social or language dysfunction, suggesting the possibility that a second hit could be involved. However, no specific ones have been identified. Modeling suggests oligogenic (2-5 genes) inheritance, possibly with interaction among the genes, although heterogeneity (different genes in different families) is also possible. Consistent with this mechanistic model, the phenotype varies in severity within families from severe autism to Asperger syndrome to milder social and language traits. The appreciation by parents of this broad range of social and language difficulties in sibs may explain, in part, the impression of an increase in prevalence. To date, at least 3 or 4 chromosomal regions of interest have been identified by one or more research groups. An understanding the neural mechanisms by which these genes act could provide opportunities for primary prevention through changes in maternal diet or physiology during pregnancy or by enabling the search for the identify of possible second hits that would increase the severity of the phenotype.
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I do not have any significant financial interest/arrangement or affiliation with any organization/institution whose products or services are being discussed in this session.