Consistent with twin studies, MD and AD show moderate overlap of genetic factors [rgMD−AD = + 0.47, 95% CI = (0.32, 0.62), P = 6.6 × 10−10] (Kendler et al., 1993; Prescott et al., 2000). A significant genetic correlation between AC-quantity and AC-frequency was observed [rgAC quantity−AC frequency = + 0.52, 95% CI = (0.48, 0.56), P = 1.3 × 10−149], but MD showed significant correlations with these traits in opposite directions [rgMD−AC quantity = + 0.14, 95% CI = (0.09, 0.20), P = 2.9 × 10−7; rgMD−AC frequency = −0.17, 95% CI = (−0.22, −0.11), P = 1.5 × 10−10].
