For other illicit drugs, significant linkage peaks have been identified on human chromosomes 9 (a region approximately 40 cM upstream of the region linked with cannabis use) and 12 for cocaine dependence (48), on chromosome 17 at 103.5 cM for a heavy-opioid-use cluster-defined trait (49), and on 14q for DSM-IV opioid dependence (79). Genome-wide linkage analysis of heroin dependence in Han Chinese reported several linkage regions, but none reached genome-wide significance (52). An analysis in families severely affected by alcohol-use disorders reported significant linkage on human chromosome 2 (LOD score of 3.2) with illicit drug dependence (1).
