Abstract and Keywords
Bipolar and unipolar mood disorders are common, chronic illnesses with high morbidity and mortality. This chapter reviews evidence of heritable components of risk from twin, family, adoption, and molecular studies. Heritability (that fraction of risk due to germline DNA variation) of bipolar disorders is estimated at 65–80%, while unipolar disorders heritability is less, ~40%. Genome-wide association studies of bipolar disorder have identified several risk alleles in brain-expressed genes, including ankyrin 3 and a subunit of an L-type calcium channel. Similar studies of unipolar disorders have yielded evidence for risk alleles, probably due to inadequate sample sizes, given the lower heritability of this disorder. Both disorders are characterized by shared genetic susceptibility with other psychiatric nosologic categories, including schizophrenia and attention deficit disorder. The molecular studies have indicated that both disorders are polygenic, with hundreds of common susceptibility alleles, each conveying a very small amount of risk.
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