One possible challenge to identification of novel loci contributing to AD susceptibility may be the heterogeneity underlying the diagnosis of AD. Meeting criteria for DSM-IV AD requires that an individual endorse any three (or more) of the seven DSM-IV criteria (Tolerance; Withdrawal; Drinking more than intended; Desire to cut drinking; Giving up activities; Time spent drinking; Drinking despite problems) during the same 12-month period. However, psychometric literature points to the differential severity and contribution of individual criteria10. An approach to reduce diagnostic heterogeneity may be the analysis of individual DSM-IV criteria in addition to the overall AD diagnosis. Twin studies have suggested that the individual criteria that comprise the AD diagnosis are heritable 11-13. For instance, Kendler and colleagues showed the heritability of individual criteria ranged from 36% (Desire to cut drinking) to 59% (Time spent drinking) 14. Another study found that heritability of individual criteria (in a subset of the data used here) were between 29% (Tolerance) and 59% (Drinking more than intended) 9. Genomic data also support this variability with Palmer et al reporting a SNP-based heritability ranging
