We compared the utility of three traits—a DSM-IV CD diagnosis and two highly heritable subtypes based on cocaine use and related behaviors—for association analysis of 130 candidate genes related to addictions in two American populations. We obtained the most significant findings in the AA population, where two SNPs exceeded the empirical significance threshold for a main effect after correction for multiple comparisons. Rs5988072 (in HTR2C) was significantly associated with both the CD diagnosis and the CD subtype of early-onset and heavy cocaine use, with high comorbidity. Rs11939815 (in CLOCK) was associated only with the CD subtype of heavy cocaine use with infrequent intravenous injection.
