INS and diabetes mellitus: Insulin-deficiency caused directly by proinsulin misfolding has been proved unequivocally in an autosomal-dominant form of diabetes known as Mutant INS-gene-induced Diabetes of Youth (MIDY) (Liu et al., 2010b), which occurs in patients bearing one mutant and one wild-type INS allele (Liu et al., 2015; Støy et al., 2010).