Moderate negative phenotypic correlations were observed between cigarette pack-years and three subcortical volumes. These associations indicate relationships between higher levels of cigarette pack-years and a reduction in volume for these specific structures. The significant phenotypic correlation between left cerebellum cortex and cigarette pack-years (rP = -0.11, p = 0.03) was largely due to genetic factors shared between the two (covA = -0.13, p = 0.04) rather than shared unique environmental factors (covE = 0.02, p = 0.68). The genetic correlation between left cerebellum cortex and pack-years was -0.28 (95% CI = -1; -0.02), indicating a moderate degree of genetic influences shared between the two. Further, these results suggest that genetic influences related to increased cigarette pack-years are expected to decrease volume in the left cerebellum cortex (Table I).
