Shared genetic susceptibility contributes modestly to major depressive disorder (MDD) and alcohol dependence (AD) comorbidity, a recent study found. Furthermore, individuals with elevated polygenic risk for MDD may also be at risk for AD. Association analyses were conducted between MDD polygenic risk score (PRS) and AD case-control status in European ancestry samples from 4 independent genome-wide association study (GWAS) data sets. Results from a meta-analysis of MDD (9,240 patients with MDD and 9,519 controls) from the Psychiatric Genomics Consortium were applied to calculate PRS at thresholds from P <.05 to P ≤.99 in each AD GWAS data set. Researchers found:

• Higher MDD PRS was associated with a significantly increased risk of AD in all samples, with stronger evidence for association after meta-analysis of the 4 samples.
• In analyses adjusted for MDD status in 3 AD GWAS data sets, similar patterns of association were observed.
• After recalculating MDD PRS using MDD GWAS data sets without comorbid MDD-AD cases, significant evidence was observed for an association between the MDD PRS and AD in the meta-analysis of 3 GWAS AD samples without MDD cases.