When WES was performed for Patient II in 2016 (after the publication of the first patients with RBCK1-related polyglucosan body myopathy), the homozygous frameshift variant NM_031229.2:c.896_899del, p.Glu299Valfs*46 in the gene RBCK1 (MIM*610924) was detected as the most likely cause of the phenotype. The gene discussed is RBCK1; the disease is polyglucosan body myopathy.