Genetics of manic depressive illness: current status and evolving concepts.

The bipolar affective spectrum is clinically heterogeneous and genetically complex. Current methods for assessment and analysis of familial traits with variable phenotypic expression and unclear mode of inheritance are reviewed. Recent evidence for a major gene localized on the X-chromosome is presented and other linkage findings are discussed. The limitations and prospects of psychiatric genetics are discussed in the light of recent advances in diagnostic nomenclature, statistical genetic techniques, and molecular biology. Methodological uncertainties notwithstanding, the powerful new techniques in genetic research portend well for unraveling the genetics of bipolar affective illness.