Glucose-6-phosphatase (G6Pase) deficiency (glycogen storage disease type 1, GSD1), also known as von Gierke disease, is one of the most severe forms of glycogen storage disease as lack of G6Pase deleteriously impacts on both gluconeogenesis and glycogenolysis. The gene discussed is G6PC1; the disease is Glycogen storage disease due to glycogenin deficiency.