GSDIX is a group of glycogenoses caused by hepatic phosphorylase kinase deficiency, a hexadecameric enzyme comprising four copies each of four unique subunits encoded by four different genes; PHKA1, PHKA2, PHKB, and PHKG2 [20,22]. This evidence concerns the gene PHKB and hyperinsulinemic hypoglycemia, familial, 4.