Our results can be usefully compared to two similar prior investigations both from the Australian Twin Registry (Grant et al., 2009; Whitfield et al., 2004). Our findings were most similar to those reported by Grant and colleagues (2009) who found, in both men and women, a very high genetic correlation between a factor derived from 5 consumption measures for the year of heaviest drinking and an AD symptom count. Although the consumption measures were not identical, and we used a dichotomous AD diagnosis and found some differences across the sexes, qualitatively both studies agreed that multiple consumption measures obtained for the period of heaviest drinking can index very closely the genetic risk for AD. Our results agree less well with the earlier report by Whitfield and colleagues (2004), which found a considerably lower genetic correlation between AC and AD. However, this study evaluated mean alcohol intake across three assessment waves rather than at the time of heaviest alcohol use, which probably explains the discrepancy in findings.
