EPM2A and glycogen storage disease due to glycogen branching enzyme deficiency: Andersen disease (MIM 232500) and adult polyglucosan body disease (APBD; MIM 263570) caused by glycogen branching enzyme (GBE1) deficiency, as well as Lafora disease (MIM 254780) due to mutations in enzymes involved in glycogen dephosphorylation (malin and laforin), are neurological diseases sharing a common neuropathology of malformed glycogen (‘polyglucosan’) accumulation.