GDH-HI (hyperinsulinism hyperammonemia syndrome; HI/HA syndrome) caused by GLUD1-activating mutations is the second most common cause of congenital hyperinsulinism (CHI MIM256450), which is a genetic and phenotypic heterogeneous group of disorders associated with dysregulated insulin secretion [1]. This evidence concerns the gene GLUD1 and congenital isolated hyperinsulinism.