G6PC3 is required for glucose homeostasis of cells, where it catalyses the hydrolysis of glucose-6-phosphate [G6P] to glucose within the endoplasmic reticulum [ER].23 Although G6PC3 is expressed ubiquitously,20 neutropenia is a consistent finding in patients with G6PC3 deficiency.24 The related syndrome glycogen storage disorder-1b [GSD-1b] also manifests neutropenia and enterocolitis24 and is caused by defects affecting the G6PC3-coupled glucose-6-phosphate transporter. The gene discussed is G6PC3; the disease is hyperinsulinemic hypoglycemia, familial, 4.