Imprinted genes and mental dysfunction

There is a rapidly accumulating body of evidence from family, adoption and twin studies suggestive of a genetic component to many common mental disord ers. In some cases, the transmission of abnormalities has been shown to be dependent upon the sex of the parent from whom they are inherited. Such 'pa rent-of-origin effects' may be explained by a number of genetic mechanisms, one of which is 'genomic imprinting. In imprinted genes one allele is sile nced according to its parental origin. This in turn means that imprinted tr aits are passed down the maternal or paternal line, in contrast to the more frequent Mendelian mode of inheritance that is indifferent to the parental origin of the allele. In the present review, we survey the evidence for th e influence of imprinted genes on a number of mental disorders, ranging fro m explicit imprinted conditions, where in some cases abnormalities have bee n mapped to particular gene candidates, to examples where the evidence for parent-of-origin effects is less strong. We also consider, briefly, the wid er implications of imprinted effects on mental dysfunction, in particular w ith respect to evolutionary pressures on mammalian brain development and fu nction.