Deficiency of glycogen branching enzyme is causative of Glycogen Storage Disease type IV (GSD-IV), a rare autosomal recessive disorder of the glycogen synthesis, characterized by the accumulation of amylopectin-like polysaccharide, also known as polyglucosan, in almost all tissues. Its clinical presentation is variable and involves the liver or the neuromuscular system and different mutations in the GBE1 gene, located on chromosome 3, have been identified in both phenotypes. This review will addresses the neuromuscular clinical variants, focusing on the molecular genetics aspects of this disorder.