DDC and Addictive alcohol use: The extreme QTL GWA analysis identified a cluster of 21 genes located on chromosome 2 L between two intergenic regions (2 L: 19,034,444 - 19,208,621) spanning from mib2 to drl and associated with variation in acute alcohol sensitivity (Additional file 8), including Catsup and Ddc, which regulate the biosynthesis of dopamine, a neurotransmitter critically associated with alcohol addiction in human studies [67, 68] and implicated in associative conditioning in Drosophila [52, 53].