Significant phenotypic correlations between cigarette pack-years and measures of subcortical volume were due to significant sharing of unique environmental factors. These relationships were detected for left accumbens (rP = -0.03, p = 0.01; covE = -0.10, p = 0.01) and left pallidum (rP = -0.07, p = 0.03; covE = -0.08, p = 0.01). Unique environmental factors involved in higher levels of cigarette pack-years were also associated with decreased volumes for these regions, as indicated by the moderate environmental correlations between smoking and left accumbens (rE = 0.24, 95% CI = -0.4; -0.05) as well as left pallidum (rE = -0.21, 95% CI = -0.38; -0.03).
