We examined the association between genetic variation in the CHRNA4 and CHRNB2 genes and ND symptoms in two sample populations: Center on Antisocial Drug Dependence (CADD) and Genetics of Antisocial Drug Dependence (GADD), described in detail below. These samples are unique because they initially represented heavy drug using adolescents who have been followed longitudinally. Our primary analysis with SNPs in CHRNA4 and CHRNB2 was performed in the CADD sample. Initial analyses were performed in non-Hispanic European Americans (EA) from each population. To increase the sample size we then included the second largest ethnic subset in our populations, individuals who self-identified as Hispanic. Since we are using family-based methods, false positive associations due to population stratification are unlikely. Following analysis in the CADD sample, we examined the GADD population as a replicate sample using only the two top SNPs found within CHRNA4.
