OPRD1 and type 2 diabetes mellitus: Of note, the 196 genes included 6 of the genes we selected for functional follow-up (BARX1, CHL1, FAIM2, HHATL, OPRD1, and PAX5 itself), and a literature search showed that approximately 25% of the 196 genes have been found to regulate β cell function and/or numbers, or have genetic variants associated with T2D or other metabolic traits in humans (Supplemental Table 11 and Figure 7A).