FBP1 and hyperinsulinemic hypoglycemia, familial, 4: GSD IX is an insidious disease and its diagnosis is complex because of the overlap of clinical phenotypes with other congenital diseases, such as other glycogenoses (GSD III, VI) or diseases related to carbohydrate metabolism (glucose-6-phosphatase deficiency and fructose-1,6-bisphosphatase deficiency).