The importance to make a rapid differential diagnosis lies in establishing the appropriate therapeutic approach, such as specific nutritional intervention regarding GSDs and FAODs type and GCK-HI, or medical therapy in case of GSD type Ib as well as HNF4a/SLC2A2 gene mutations, which share a similar phenotype but different treatment, or surgical strategies in case of focal-HI. The gene discussed is HNF4A; the disease is glycogen storage disease Ib.