INS and diabetes mellitus: Syndromic forms of diabetes can derive from severe defect of either insulin secretion (e.g., Wolfram syndrome, Wolcott–Rallison syndrome, thiamine-responsive megaloblastic anemia, mitochondrial mutations) or insulin action (i.e., insulin receptor mutations, Bardet–Biedl syndrome, Alstrom syndrome, Berardinelli–Seip congenital lipodystrophies) [5,24].