There is shared genetic risk for dependence on multiple substances, and the nicotinic receptor gene cluster on chromosome 15 harbors multiple polymorphisms that associate to this risk. Here, we report the results of an association study with 21 SNPs genotyped across the CHRNA5, CHRNA3, and CHRNB4 loci on chromosome 15q25.1. The sample consists of a discovery set (N=1858) of European-American and African-American (AA) families, ascertained on the basis of a sibling pair with cocaine and/or opioid dependence, and a case-control replication sample (N=3388) collected for association studies of alcohol, cocaine, and opioid dependence. We tested the SNPs for association with lifetime cocaine, opioid, nicotine, and alcohol dependence. We replicated several previous findings, including associations between rs16969968 and nicotine dependence (P=0.002) and cocaine dependence (P=0.02), with opposite risk alleles for each substance. We observed these associations in AAs, which is a novel finding. The strongest association signal in either sample was between rs684513 in CHRNA5 and cocaine dependence (OR=1.43, P=0.0004) in the AA replication set. We also observed two SNPs associated with alcohol dependence, that is, rs615470 in CHRNA5 (OR=0.77, P=0.0006) and rs578776 (OR=0.78, P=0.001). The associations between CD and rs684513, AD and rs615470, and AD and rs578776 remained significant after a permutation-based correction for multiple testing. These data reinforce the importance of variation in the chromosome 15 nicotinic receptor subunit gene cluster for risk of dependence on multiple substances, although the direction of the effects may vary across substances.
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