Glycogen storage disease type V (GSDV) (OMIM#232600), also known as McArdle disease, is a rare autosomal recessive myopathy caused by biallelic pathogenic mutations in the PYGM gene [1] that result in deficiency of the skeletal muscle isoform of glycogen phosphorylase (or ‘myophosphorylase’, PYGM) [2]. Here, PYGM is linked to glycogen storage disease V.