GSD-Ia is caused by a deficiency in the liver/kidney/intestine-restricted G6Pase-alpha (G6PC) while GSD-Ib is caused by a deficiency in the ubiquitously expressed G6PT (or SLC37A4) (PMID:25288127). A new framework has now emerged which shows that the G6PT/G6Pase-alpha complex (GSD-Ia) maintains interprandial glucose homeostasis whereas the G6PT/G6Pase-beta complex (GSD-Ib) maintains neutrophil homeostasis and function (PMID:20975743).
G6PT is essential to maintain both interprandial blood glucose homeostasis and myeloid cell energy homeostasis, making GSD-Ib both a metabolic and immune disorder. To date, 92 separate mutations have been
identified in the SLC37A4 gene of GSD-Ib and non-GSD-Ia patients. One underlying cause of neutrophil/macrophage dysfunction in GSD-Ib and GSD-Irs (GSD-I related syndrome, Orphanet:331176) is a disturbance in ER energy homeostasis caused by a loss of G6Pase-beta (G6PC3)/G6PT-mediated glucose/G6P recycling (PMID:25288127).