Although a large number of genetic loci potentially moderating smoking have been tested, only a few have been convincingly replicated. So far, the strongest evidence of association is for CHRNA5-CHRNA3-CHRNB4 gene-cluster on chromosome 15q25(3, 6–10). Another chromosome region that has been linked with nicotine use is the TTC12-ANKK1-DRD2 gene-cluster on chromosome 11q23(11–13), although evidence here is less consistent.
