Data on 430 EA college students aged 18–22 years were drawn from the Duke Neurogenetics Study (DNS (39); Supplemental Text). First, we examined the association between genotype (rs1409568, modeled as C-allele carriers vs. T allele homozygotes) and (a) cannabis use (ever used and frequency of use in ever users) and (b) regional brain volume. A Generalized Linear Model in SPM8 was used to test whether genotype predicted regional volume within 6 brain regions (i.e., left and right amygdala, hippocampus, striatum) previously associated with cannabis use and misuse (14;15). Familywise error correction (FWE p < .05) with a 10-voxel extent cluster threshold was applied to each of these 6 anatomical regions of interest (ROIs) derived from the Automated Anatomical Labeling atlas (40) within Wake Forest University Pick Atlas software (41). Additional methodological details are presented in Supplemental Text. Second, we tested whether cannabis use (ever used; frequency of use in ever users) was associated with regional gray matter volume in any of these regions. Third, we examined whether associations between genotype and regional brain volume persisted after controlling for cannabis use.
