GCK and diabetes mellitus: So for as the clinical complications of GCK mutations are concerned, activating and heterozygous mutations results in persistent hyperinsulinemic hypoglycemia of infants (PHIH), while as homozygous mutations in both the alleles can result in permanent neonatal diabetes mellitus (PNDM) and mutations in single allele can result in GCK-MODY (76–78).