GPR139 has been associated with a range of specific phenotypes observed across major depressive disorder (MDD), schizophrenia, and attention-deficit/hyperactivity disorder (ADHD), including insomnia, lateral ventricle volume changes, and alcohol abuse (refer to Table 1 for the included EBI GWAS accession IDs), suggesting that GPR139 is a potential therapeutic target for these neuropsychiatric disorders and their comorbidities. This evidence concerns the gene GPR139 and major depressive disorder.