ADH4 encodes alcohol dehydrogenase 4, a class II NAD-dependent enzyme with multiple metabolic functions. Primarily, ADH4 catalyzes oxidation of retinoids, converting all-trans-retinol and 9-cis-retinol to their aldehyde forms 1, and oxidizes long-chain omega-hydroxy fatty acids such as 20-HETE to dicarboxylic acids 2. The gene spans 21 kb with nine exons and exhibits different regulatory mechanisms compared to class I ADH genes 3. ADH4 promoter polymorphisms significantly affect gene expression, with the -75A allele showing over twofold greater promoter activity than the -75C allele 4. Clinically, ADH4 genetic variation associates with alcohol dependence and drug dependence in European Americans through recessive inheritance patterns, with SNP rs1042363 and rs1800759 showing strongest associations 56. Recent evidence identifies ADH4 as a potential prognostic biomarker in hepatocellular carcinoma, where low ADH4 expression correlates with poor outcomes and immune cell infiltration patterns, suggesting therapeutic targeting opportunities 7. However, ADH4 polymorphisms show no significant association with cluster headache susceptibility across ethnic populations 89.