Bipolar affective disorder in a genetic isolate

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Bipolar affective disorder (BP), or manic-depressive illness, is a major cause of disability and mortality worldwide. It has a lifetime prevalence of about 1% and suicide risk of about 20%. The disorder is characterised by episodes of mania or hypomania and depression, appearing in varying succession, with or without intermission. Twin, family, and adoptive studies point to a strong genetic component leading to the development of bipolar disorder, with a heritability of the order of 80%. Yet the identification of the genetic basis of the disease has proved exceedingly difficult, with numerous studies producing no definitive data. The lack of convincing results has been interpreted as an indication of complex genetic mechanisms and underlying differences between affected families and ethnic groups. Genetically isolated populations, where most individuals descend from a small number of founders, are believed to hold great potential for understanding the genetic basis of complex diseases, such as bipolar disorder. Affected subjects in such populations are likely to share the same predisposing genes, making these genes easier to identify. During the last 10 years, we have been involved in the study of bipolar disorder in one such population, with very promising results. In this project, we propose to take the research further by collecting more affected families, confirming the current positive findings and narrowing down the search to a small region, possibly a single gene. If successful, the study will be a major breakthrough which, by identifying a molecular pathway and disease mechanism, will contribute valuable and generally valid information on the biological basis of mood disorders.