heritability are attributable to PTSD and/or AD. As GWAS sample sizes for AD increase, male and female specific AD heritability estimates and genetic correlations with PTSD should be examined. The current study relies on summary statistics from the two largest initiatives to examine DSM diagnoses of PTSD and AD, however ongoing efforts to examine non-diagnostic, quantitative phenotypes (e.g., frequency/quantity of drinking) and other substance use disorders (cannabis, opioids) will provide important extensions to this work. Finally, the reason for differences in heritability across the male PTSD sub-samples, which impacted estimation of genetic correlation (i.e., as a genetic correlation can only be estimated in the presence of heritability), remains unknown at present. However, it is hypothesized to be due to differences between the PGC1.5 cohorts and UK Biobank (see supplemental material for more details on the samples). Specifically, one way in which these two samples notably differ is in trauma type, which is known to be heterogeneous. In the PGC1.5, a substantial proportion of men were from military cohorts and most women were civilian samples, while the UKB cohort had few to no participants exposed to military-related trauma (Nievergelt et al., 2019). Other sample differences include measurement/diagnosis of the PTSD phenotype
