Evidence of susceptibility loci on 4q32 and 16p12 for bipolar disorder

We performed a genome-wide scan for susceptibility loci in bipolar disorder in a study sample colleted from the isolated Finnish population, consisting of 41 families with at least two affected siblings. We identified one distinct locus on 16p12 providing significant evidence for linkage in two-point analysis (Z(max)=3.4). Furthermore, three loci with a two-point LOD score >2.0 were observed with markers on 4q32, 12q23 and Xq25, the latter locus having been earlier identified in one extended Finnish pedigree. In the second stage we fine mapped these chromosomal regions and also genotyped additional family members. In the fine mapping stage, 4q32 provided significant evidence of linkage for the three-point analyses (Z(max)=3.6) and 16p12 produced a three-point LOD score of 2.7. Since the identified chromosomal regions replicate earlier linkage findings in either bipolar disorder or other mental disorders, they should be considered good targets for further genetic analyses.