Some genes may contribute to an increased susceptibility to addictions in general. One study used a staged meta-analysis to explore comorbid alcohol and nicotine dependence and detected genome-wide evidence of association with SNPs spanning a region on chromosome 5 that includes both IPO11 (importin 11) and HTR1A (5-hydroxytryptamine (serotonin) receptor 1A, G protein-coupled)78. Importins are involved in transport of proteins and RNA between nucleus and cytoplasm, and serotonin has been implicated in many neural processes; HTR1A agonists reduce the anxiety-like behavior induced by repeated ethanol withdrawals in rats79. Analyses of RNA expression in lymphoblastoid cell lines suggested that SNPs within this region on chromosome 5 had cis-acting regulatory effects on the expression of HTR1A or IPO11.
