RBCK1 and disorder of glycogen metabolism: Polyglucosan body disease (PBD) is a type of glycogen storage disease (GSD) and is mainly caused by mutations in eight different human genes, namely, GYG1, GBE1, RBCK1, PFKM, EPM2A, EPM2B (NHLRC1), PRDM8, and PRKAG2 [1].