SLC37A4 and lactic acidosis: Glycogen storage disease type Ib (GSDIb) (OMIM 232220) is an ultrarare inherited disorder affecting glycogenolysis and gluconeogenesis, with an incidence of approximately 1 in 500 000.1 It stems from variants in the SLC37A4 gene, which produces glucose-6-phosphate transporter.2 Symptoms of GSDIb include hepatomegaly, nephromegaly, fasting hypoglycemia, lactic acidosis, hyperuricemia, and hyperlipidemia.