Numerous studies have suggested, and twin studies (22) established, that the genetic contributions to risk for substance dependence are both shared (i.e., common to multiple substances) and specific (i.e., applicable to only one substance). POMC, which encodes several peptides (including ACTH and β-endorphin), can be viewed as, potentially, a common susceptibility gene for substance dependence disorders. To date, one family-based study (23) has demonstrated an association between POMC variants (two SNPs in intron 1) and opioid dependence, and one case-control-based study (24) (by haplotype analyses) has provided evidence for a sex-specific role of POMC in ethanol preference and dependence.
