POLR2D and type 2 diabetes mellitus: Most of the differentially expressed genes are of unknown function in β cells, but some have been clearly associated with insulin secretion (for examples, GLUT2 (ref. 16), PPP1R1A17 and ABCC9/SUR2 (ref. 18)) or are known to be dysregulated in T2D (for examples, G6PC2 (ref. 19, RPB4 (ref. 20) and MAFB21).