Localization of bipolar susceptibility locus by molecular genetic analysis of the chromosome 12q23-q24 region in two pedigrees with bipolar disorder and Darier's disease.

Objective: The authors previously reported two families (pedigrees 324 and 5501) in which Darier's disease-a rare, autosomal dominant skin disease-and bipolar disorder cosegregate. In each of these families there is complete cosegregation of mood disorder with a segment of chromosome 12q23-q24, consistent with the existence of a highly penetrant dominant variant. Here molecular genetic analyses aimed at localizing and identifying the susceptibility gene in this region are reported.

Method: In the two families, the authors undertook 1) linkage and haplotype studies using 45 highly polymorphic molecular genetic markers in order to delineate the region of interest and 2) direct analysis of genes within this region.

Results: Linkage and haplotype information from the most severely affected individuals defined a region of interest that spanned two neighboring regions of 19 megabases (Mb) (D12S362-D12S1646) and 7 Mb (D12S1718-D12S837). Information from all individuals refined the region of interest to 6.5 Mb (D12S127-D12S1646). Systematic study of the coding and flanking intronic regions of 25 known genes within this latter region failed to identify any highly penetrant autosomal dominant disease-conferring mutations in these pedigrees.

Conclusions: This linkage and haplotype analysis, together with data from several other linkage studies, provides compelling evidence for the existence in the 12q23-q24 region of one or more genes involved in the pathogenesis of bipolar disorder. Further molecular genetic analysis of this region is required to identify the gene(s).