G6PC1 and glycogen storage disease Ib: Glycogen storage disease (GSD) is a rare, inherited metabolic disorder that causes improper glycogen storage in the body, primarily in the liver and/or muscles.[1] The overall incidence of GSD is estimated to be 1 in 20 000–43 000 live births.[2] Mutations in the gene encoding glucose‐6‐phosphatase (G6PC) cause GSD type Ia (GSD‐Ia), while mutations in glucose‐6‐phosphate translocase (G6PT/SLC37A4) cause GSD type Ib (GSD‐Ib).