There is new evidence that nicotine dependence and schizophrenia share contributory genetic factors. Recently, the Psychiatric Genetics Consortium identified 128 independent loci that contribute to risk of developing schizophrenia (Schizophrenia Working Group of the Psychiatric Genomics Consortium, 2014). Interestingly, one locus recently identified as contributing to schizophrenia is the chromosome 15q24 locus, which contains the α5-α3-β4 nicotinic receptor subunit genes and is the strongest genetic contributor to nicotine dependence (Hancock et al., 2015; TAG, 2010). Although this is promising evidence of shared genetic factors between nicotine dependence and schizophrenia, because the analysis did not adjust for smoking, the finding may be due to confounding from smoking. A different study found positive associations both between nicotine dependence and polygenic risk scores for schizophrenia, and between schizophrenia and polygenic risk scores for cotinine levels (Chen et al., 2016). These complimentary analyses support the hypothesis that nicotine dependence and schizophrenia have shared genetic factors.
