Follow-up analyses investigating the inter-relationships between these 3 CNR1 tSNPs on lobar WM volumes across patients with versus without marijuana misuse are summarized in Table 4. Compared to rs12720071-A homozygotes, G-allele carriers had significantly smaller frontal and temporal WM volumes (p≤.05; Table 4 and Figures 3a and 3b). Most interestingly, there were significant rs12720071-genotype-by-marijuana misuse interaction effects on parietal WM volumes (p=.05; Table 4), which are suggestive of gene×environment interactions for conferring brain volume deficits in schizophrenia. rs12720071-G-allele carriers with marijuana abuse/dependence had the smallest mean parietal WM volumes than the other 3 subgroups (i.e. patients without marijuana abuse/dependence and rs12720071-A homozygotes with marijuana abuse/dependence; Figure 3c). Temporal and parietal WM volumes in rs7766029-C homozygotes were significantly smaller than WM volumes in rs7766029-T-allele carriers (p≤.05; Table 4 and Figure 4). rs9450898-C homozygotes had significantly smaller frontal and parietal WM volumes than T-allele carriers (p≤.05; Table 4 and Figure 4).
