Loss-of function studies suggest that GLIS3 encodes a transcription factor critical for regulating the expression of insulin and several key islet-transcription factors, and may confer risk for both T1D and T2D by resulting in diminished β-cell numbers and by promoting the formation of a pro-apoptotic splice variant of the protein Bim (Kang et al., 2009; Nogueira et al., 2013; ZeRuth et al., 2013). This evidence concerns the gene GLIS3 and type 1 diabetes mellitus.