is expected and has been observed in the literature for many other phenotypes (Vischer, Brown, McCarthy, & Yang, 2012), purported due to factors such as many more variants still needing to be identified, requiring larger GWAS samples; rare variants and structural variation that are not typically captured in existing genotypic arrays; low power to detect gene-gene interactions; and not accounting for shared environment among relatives (Manolio et al., 2009). Given the small heritability estimates, this correlation represents only a proportion of the heritability that overlaps between AD and PTSD. It is also noted that findings highlight the unique genetic influence for each trait (i.e., two thirds of the genetic risk is unique to each disorder). Overall, study findings are highly consistent with other molecular genetic studies of AD (Walters et al., 2018) and PTSD (Sumner et al., 2017) and related traits, and align with the twin literature on shared heritability (e.g., Sartor et al., 2011).
