Glycogen storage disease type V

Glycogen storage disease type V is a metabolic disorder, more specifically a glycogen storage disease, caused by a deficiency of myophosphorylase.

GSD type V is also known as McArdle's disease or muscle phosphorylase deficiency. The disease was first reported in 1951 by Dr. Brian McArdle of Guy's Hospital, London.

People with this disease experience difficulty when their muscles are called upon to perform relatively brief yet intense activity. The inability to break down glycogen into glucose results in an energy shortage within the muscle, resulting in muscle pain and cramping, and sometimes causing serious injury to the muscles. The typical features of McArdle disease include exercise intolerance with myalgia, early fatigue, and stiffness of exercising muscles, which are sometimes relieved by rest. Following a short period of rest, most patients experience a second wind and can resume exercise with less difficulty.The prevailing levels of fatty acids as potential energy sources for muscle may account for the second wind phenomenon. In addition, rhabdomyolysis&mdash;the breakdown of muscle tissue&mdash;can cause myoglobinuria, a red-to-brown-colored urine. The myoglobinuria can cause kidney damage. The disease is hereditary and is inherited as an autosomal recessive trait. Anaerobic exercise must be avoided but regular gentle aerobic exercise is beneficial.