Background: Alcohol dependence is more common among men than among women. Potential explanations for this include the role of genes in sex chromosomes (X and Y). In the present study, we scanned the entire Y chromosome and its homologs on the X chromosome in men to identify male-specific risk genes for alcohol dependence.
Methods: Two thousand nine hundred and twenty-seven individuals in two independent cohorts were analyzed. The European-American male cohort (883 cases with alcohol dependence and 445 controls) served as the discovery cohort and the European-American female cohort (526 cases and 1073 controls) served as a contrast group. All individuals were genotyped on the Illumina Human 1M beadchip. Two thousand two hundred and twenty-four single nucleotide polymorphisms (SNPs) on the Y chromosome or in the homologs on the X chromosome were analyzed. The allele frequencies were compared between cases and controls within each cohort using logistic regression analysis.
Results: We found that, after experiment-wide correction, two SNPs on the X chromosome were associated significantly with alcohol dependence in European-American men (P = 1.0 × 10 for rs5916144 and P = 5.5 × 10 for rs5961794 at 3' UTR of NLGN4X), but not in the women. A total of 26 SNPs at 3'UTR of or within NLGN4X were nominally associated with alcohol dependence in men (5.5 × 10 ≤ P ≤ 0.05), all of which were not statistically significant in women.
Conclusion: We conclude that NLGN4X was a significant male-specific risk gene for alcohol dependence in European-Americans. NLGN4X might harbor a causal variant(s) for alcohol dependence. A defect of synaptogenesis in neuronal circuitry caused by NLGN4X mutations is believed to play a role in alcohol dependence.