Because exposure to a substance is a necessary step in the development of SUD, we next included exposure data for the three classes of SUD. For AD, we used the question “have you ever drank alcohol?” as the determinant of exposure for our model. For ND, we used two different levels of exposure. The first level of exposure was the question “Have you ever smoked?”. The second more stringent level was determined by their response to the question “In your lifetime, have you smoked 100 cigarettes?” Once again, inclusion of this data strengthened the significance of the associations for both AD and ND (Table V). Interestingly, the effects of GABRA2 haplotype were again markedly more pronounced in the female subjects than in the male subjects.
