Expression and functional assessment of candidate type 2 diabetes susceptibility genes identify four new genes contributing to human insulin secretion

•Expression of genes located nearby T2D associated signals is enriched in β cells.•Knockdown of 7 T2D genes with known role in β cell changes insulin secretion.•Knockdown of 4 T2D genes with unknown role in β cell impairs insulin secretion.•RNA-seq in cells with knockdown of these 4 genes detected T2D-related networks.