Medical disorders that occur in the context of substance dependence seem to have genetic associations that are not entirely explained by the contribution of the genetic variant to substance use. Specifically, gene variants in ADH were protective for cancers of the upper aerodigestive tract, even after adjusting for alcohol consumption. Similarly, SNPs correlated with rs16969968 are associated with an increased risk of COPD and lung cancer, after adjusting for cigarette use. Although the interpretation of these studies is difficult because of the confounding between the medical illness and substance exposure, there is evidence of a genetic interaction in both cases.
