Bipolar disorder: from families to genes.

BACKGROUND Genetic factors are known to contribute to the etiology of bipolar illness, but the actual genetic mechanisms remain to be clarified. METHODS This paper reviews the research undertaken to establish the genetic basis of bipolar illness and to elucidate the nature of its genetic predisposition. RESULTS The presented findings suggest that bipolar affective disorder is a heterogeneous condition characterized by a complex relationship between the genetic susceptibility and the clinical presentation. Linkage studies have generated promising and replicated findings on chromosomes 18 and 21. CONCLUSION In spite of the methodological difficulties inherent in the genetic study of psychiatric disorders recent investigations have made important advances and promise to identify specific susceptibility genes.