In this study, the authors report on five Sardinian patients presenting in their 5th or 6th decade with progressive limb girdle muscle weakness but with muscle biopsies demonstrating vacuolar myopathy. The more or less abundant subsarcolemmal and intermyofibrillar vacuoles showed intense, partially α-amylase resistant, PAS-positive deposits consistent with polyglucosan. The recent description of late-onset polyglucosan myopathy prompted them to find new genetic defects in the gene (GYG1) encoding glycogenin-1, the crucial primer enzyme of glycogen synthesis in muscle. A single homozygous intronic mutation harboured by five patients was identified.
