Update on new muscle glycogenosis

Abstract

The field of muscle glycogenoses has progressed in recent years by the identification of new disorders, and by reaching a better understanding of pathophysiology of the disorders and the physiology of glycogen metabolism. In this review, we describe the clinical and pathological features of the three most recently described muscle glycogenoses caused by recessive mutations in GYG1, RBCK1 and PGM1. The three involved enzymes play different roles in glycogen metabolism. Glycogenin-1 (GYG1) is involved in the initial steps of glycogen synthesis, whereas phosphoglucomutase catalyzes two metabolic pathways; the connection between galactose and glycogen on one side, and glucose metabolism on the other side. The metabolic consequences of mutations in the ubiquitin ligase gene RBCK1 are still poorly understood. GYG1 deficiency has been associated with cardiomyopathies with abnormal storage material in the heart, but most cases present with a polyglucosan body myopathy without cardiac involvement. The recent identification of new glycogenosis not only allows to improve the knowledge of glycogen metabolism, but also builds bridges with protein glycosylation and immune system.