AbstractMcArdle disease is an autosomal recessive disorder caused by the absence of the muscle glycogen phosphorylase, which leads to impairment of glycogen breakdown. The McArdle mouse, a model heavily affected by glycogen accumulation and exercise intolerance, was used to characterize disease progression at three different ages. The molecular and histopathological consequences of the disease were analyzed in five different hind-limb muscles (soleus, extensor digitorum longus, tibialis anterior, gastrocnemius and quadriceps) of young (8-week-old), adult (35-week-old) and old (70-week-old) mice. We found that McArdle mice have a high perinatal and post-weaning mortality. We also observed a progressive muscle degeneration, fibrosis and inflammation process that was not associated with an increase in muscle glycogen content during aging. Additionally, this progressive degeneration varied among muscle and fiber types. Finally, the lack of glycogen content increase was associated with the inactivation of glycogen synthase and not with compensatory expression of the Pygl and/or Pygb genes in mature muscle.