Glycogen storage disease type V
Glycogen storage disease type V (GSD5, GSD-V), also known as McArdle's disease, is a metabolic disorder, one of the metabolic myopathies, more specifically a muscle glycogen storage disease, caused by a deficiency of myophosphorylase. Its incidence is reported as one in 100,000, roughly the same as glycogen storage disease type I.
| Glycogen storage disease type V | |
|---|---|
| Other names | McArdle disease, muscle glycogen phosphorylase (myophosphorylase) deficiency |
| Muscle biopsy specimen showing vacuolar myopathy: The patient had a type V glycogenosis (McArdle disease) | |
| Specialty | Neuromuscular medicine |
| Symptoms | Exercise intolerance, inappropriate rapid heart rate response to exercise, exaggerated cardiorespiratory response to exercise, exercise-induced premature muscle fatigue and cramping, second wind phenomenon |
| Complications | Poor physical or mental health due to prolonged delay in diagnosis, misdiagnosis, or having been given inappropriate exercise advice. Rare complications include rhabdomyolysis with myoglobinuria requiring hospitalization, transient muscle contracture, and compartment syndrome. |
| Usual onset | Childhood-onset (median age of symptom onset 3 years) |
| Causes | Pathogenic autosomal recessive mutations in PYGM gene coding for myophosphorylase |
| Diagnostic method | Genetic testing (preferred), muscle biopsy. Supplemental tests: blood tests, exercise stress test, 12-Minute Walk Test, non-ischemic forearm test, EMG |
The disease was first reported in 1951 by Dr. Brian McArdle of Guy's Hospital, London.
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