Glycogen storage disease type V
| Glycogen storage disease type V | |
|---|---|
 |
|
| Muscle biopsy specimen showing vacuolar myopathy. The patient had a type V glycogenosis (McArdle Disease) | |
| Classification and external resources | |
| Specialty | endocrinology |
| ICD-10 | E74.0 |
| ICD-9-CM | 271.0 |
| OMIM | 232600 |
| DiseasesDB | 5307 |
| MedlinePlus | 000329 |
| eMedicine | med/911 |
| MeSH | D006012 |
| GeneReviews | |
Glycogen storage disease type V (GSD-V) is a metabolic disorder, more specifically a glycogen storage disease, caused by a deficiency of myophosphorylase. Its incidence is reported as 1 in 100,000, approximately the same as glycogen storage disease type I.
GSD type V is also known as McArdle disease or muscle phosphorylase (myophosphorylase) deficiency. The disease was first reported in 1951 by Dr. Brian McArdle of Guy's Hospital, London.
The onset of this disease is usually noticed in childhood, but often not diagnosed until the third or fourth decade of life. Symptoms include exercise intolerance with muscle pain, early fatigue, painful cramps, and myoglobin in the urine (often provoked by a bout of exercise). Myoglobinuria may result from the breakdown of skeletal muscle known as rhabdomyolysis, a condition in which muscle cells breakdown, sending their contents into the bloodstream.
Patients may exhibit a “second wind” phenomenon. This is characterized by the patient’s better tolerance for aerobic exercise such as walking and cycling after approximately 10 minutes. This is attributed to the combination of increased blood flow and the ability of the body to find alternative sources of energy, like fatty acids and proteins. In the long term, patients may exhibit renal failure due to the myoglobinuria, and with age, patients may exhibit progressively increasing weakness and substantial muscle loss.
Patients may present at emergency rooms with severe fixed contractures of the muscles and often severe pain. These require urgent assessment for rhabdomyolysis as in about 30% of cases this leads to acute renal failure. Left untreated this can be life-threatening. In a small number of cases compartment syndrome has developed, requiring prompt surgical referral.
There are two autosomal recessive forms of this disease, childhood-onset and adult-onset. The gene for myophosphorylase, PYGM (the muscle-type of the glycogen phosphorylase gene), is located on chromosome 11q13. According to the most recent publications, 95 different mutations have been reported. The forms of the mutations may vary between ethnic groups. For example, the R49X (Arg49Stop) mutation is most common in North America and western Europe, and the Y84X mutation is most common among central Europeans.
...
Wikipedia