CHRNA5 and nicotine dependence: In previous years genome-wide association studies and some meta-analyses have reported associations between single nucleotide polymorphisms (SNPs) in the CHRNA5-CHRNA3-CHRNB4 nicotinic acetylcholine receptor (nAChR) gene cluster on chromosome 15q 24-25 and some phenotypes describing smoking behavior like ever smoking [7], cigarettes per day (CPD) [6–20], ND defined by the Fagerström Test for Nicotine Dependence (FTND) [4, 5, 7, 11, 14, 21–29], and age at smoking initiation [27, 30, 31].