In the diplotype regression model we found a H.S. peer smoking by the AA/CC rs16969968/rs578776 diplotype interaction (p = 0.01). As illustrated in figure 2 H.S. peer smoking had a significantly lower impact on probability of nicotine dependence for those with AA/CC diplotype – the only observed diplotype that involves the high-risk AA genotype at rs16969968 – compared with other diplotypes. The variance in nicotine dependence attributable to H.S. peer smoking (R2) was more than four times lower among those with the AA/CC diplotype than all the other diplotypes combined: AA/CC = 2.7%, all other diplotypes = 12.5%; z = 2.98, p = 0.001. These results are consistent with the H.S. peer smoking by rs16969968 analysis and suggest that accounting for this SNP’s linkage disequilibrium relationship with rs578776 does not meaningfully alter the interpretation of the primary results.
