SLC6A3 and type 2 diabetes mellitus: Therefore, this study took advantage of an extensively genotyped familial cohort of T2D patients and related controls, the Diabetes Heart Study (DHS) – Mind, to investigate the role of sequence variants in genes linked to DA metabolism (e.g., DDC, TH, DRD2, DRD3, and DAT1) and associated pathways in cognitive function.