Confirmation and fine mapping of the chromosome 1 alcohol dependence risk locus

Two previous large genetic linkage studies in the US population have implicated an area in chromosome 1p to contain a susceptibility gene for alcohol dependence. The 1-LOD support interval of the linkage signal spans about 30 cM and contains >30000000 DNA base pairs (bp) and 700 predicted genes. In order to reduce the size of the candidate area and potentially identify novel candidate genes within this region, we fine-mapped this area using closely spaced short tandem repeat (STR) markers and the transmission disequilibrium test (TDT) in small nuclear families. The subjects were 87 European-American families including one or more alcohol-dependent offspring (93 children and 174 parents). The initial marker set consisted of 30 STR markers, spanning the Marshfield map interval between 101.48 and 130.73 cM. Using the TDTPHASE program, we identified three markers in the distal part of this region (125-126 cM), which showed evidence of transmission disequilibrium. On the basis of this result, an additional 12 STR markers were genotyped in this region; some of these markers provided additional evidence for linkage disequilibrium. The strongest evidence for transmission disequilibrium was obtained at the marker D1S406 (P=0.005, 126.16 cM), with supporting evidence from three neighboring STR markers D1S424 (126.16 cM, P=0.01), D1S2804 (126.16 cM, P=0.04), and D1S2776 (126.16 cM, P=0.02), which are all located within a <350000 bp interval. These findings suggest that a gene (or genes) causing susceptibility to alcohol dependence resides near location 126.16 cM on chromosome 1. In addition, these results provide independent confirmation of the linkage finding regarding the identification of at least one gene in this region increasing the risk for alcohol dependence.