GAD2 and type 1 diabetes mellitus: In patients affected by type 1 diabetes clinical intervention studies with vitamin D3 or hydroxylated analogs have been disappointing, as no clinical study has demonstratedan effect of vitamin D in ameliorating glucose metabolism and insulin secretion [113,114], however, in a small prospective trial in children with type 1 diabetes autoantibodies 1,25(OH)2D3 administration decreased the serum glutamic acid decarboxylase 65 (GAD65) autoantibody, pointing to some immunomodulation of 1,25(OH)2D3 [115].