Glycogen storage disease type I (GSD-I) consists of two subtypes: GSD-Ia, a deficiency in glucose-6-phosphatase-α (G6Pase-α) and
GSD-Ib, which is characterized by an absence of a
glucose-6-phosphate (G6P) transporter (G6PT). A third disorder, G6Pase-β deficiency, shares similarities with this group of diseases. G6Pase-α and G6Pase-β are G6P
hydrolases in the membrane of the endoplasmic reticulum, which depend on G6PT to transport G6P from the cytoplasm into the lumen. A functional complex of G6PT and G6Pase-α maintains interprandial
glucose homeostasis, whereas G6PT and G6Pase-β act in conjunction to maintain neutrophil function and homeostasis. Patients with GSD-Ia and those with
GSD-Ib exhibit a common metabolic phenotype of disturbed
glucose homeostasis that is not evident in patients with G6Pase-β deficiency. Patients with a deficiency in G6PT and those lacking G6Pase-β display a common myeloid phenotype that is not shared by patients with GSD-Ia. Previous studies have shown that neutrophils express the complex of G6PT and G6Pase-β to produce endogenous
glucose. Inactivation of either G6PT or G6Pase-β increases neutrophil apoptosis, which underlies, at least in part, neutrophil loss (
neutropenia) and dysfunction in
GSD-Ib and G6Pase-β deficiency. Dietary and/or
granulocyte colony-stimulating factor therapies are available; however, many aspects of the diseases are still poorly understood. This Review will address the etiology of GSD-Ia,
GSD-Ib and G6Pase-β deficiency and highlight advances in diagnosis and new treatment approaches, including gene therapy.