Erlich PM, Hoffman SN, Rukstalis M, Han JJ, Chu X, Linda Kao WH, Gerhard GS, Stewart WF, Boscarino JA. Nicotinic acetylcholine receptor genes on chromosome 15q25.1 are associated with nicotine and opioid dependence severity. Hum Genet. 2010 Nov; 128(5):491-9.