These externalizing disorders are also heritable (Krueger et al., 2002), with heritability estimates highest for ADHD, ranging from 70–90%, (Brikell, Kuja-Halkola, & Larsson, 2015). Heritability of CD and ODD is slightly lower, ranging from 50–80% for CD (Porsch et al., 2016) and 61% for ODD (Coolidge, Thede, & Young, 2000). Thus, it is possible that these disorders were inherited from one or both parents. In summary, these externalizing disorders observed in PAE offspring could be due to (1) direct exposure to alcohol during fetal development, inherited factors associated with (2) alcohol dependence or (3) externalizing disorders in the mother or father, or some combination, or (4) a gene by environment interaction due to an AD mother consuming alcohol while pregnant (Figure 1).
