Since we have proved the regulatory role of FKBP5 on FOXO1 phosphorylation at Ser256, which mediates the subcellular localization of the protein, this result suggested that the decrease of FKBP5 expression in β cells in T2D may be responsible for the increased nucleus translocation of FOXO1 and the subsequent loss of cytoplasmic expression of FOXO1. This evidence concerns the gene FOXO1 and type 2 diabetes mellitus.