MTNR1B and type 2 diabetes mellitus: Here, we aimed to gain further insight into the effects of MTNR1B variations on type 2 diabetes and type 2 diabetes endophenotypes by comprehensively examining coding MTNR1B variants through combining genetic association studies of quantitative traits from the UK Biobank and Danish cohorts, and through a recall-by-genotype investigation of selected MTNR1B variants.