Glycogen storage type Ib (GSDIb) is a rare inborn error of metabolism (prevalence 1:500,000) (1) caused by recessive mutations of glucose-6-phosphate translocase (SLC37A4), which encodes the glucose-6-phosphate transporter (G6PT) located in the membrane of the endoplasmic reticulum. The gene discussed is SLC37A4; the disease is glycogen storage disease Ib.