We did not find any significant difference in distribution of comorbid psychiatric diagnoses between the unaffected and alcohol dependent groups in this dataset except cannabis dependence (Table 1). Comorbid psychotic disorders (e.g., schizophrenia or schizoaffective disorder) do not appear in the dataset because they are one of the exclusion criteria for subject recruitment. To test whether comorbid psychiatric disorders contribute to the association, we performed additional FBATs with these SNPs in GRM8 using comorbid psychiatric diagnoses as phenotypes. The results were all not significant (p>0.05) except some weak association (p<0.05) of major depressive disorder, cannabis dependence, and social phobia with only 1 SNP, rs2299495. The results suggest that the association we found among the 3 SNPs in the intron 6 region of GRM8, rs1361995, rs10487457, rs10487459, is rather specific to alcohol dependence.
