Glycogen Storage Disease Type V
Also known as: McArdle disease, myophosphorylase deficiency, GSD5
Gene: PYGM
Protein: glycogen phosphorylase, muscle form
Clinical Characteristics
- Exercise intolerance with isometric or sustained aerobic exercise:
- Rapid fatigue
- Muscle pain and cramps
- 鈥淪econd wind鈥 phenomenon, or relief of pain and fatigue after a few minutes of rest
- Onset in second or third decade of life
- Muscle weakness:
- Nonprogressive muscle weakness in one third of affected individuals
- Progressive weakness in some affected individuals in the sixth or seventh decade of life
- Myoglobinuria in about 50% of affected individuals, can result in acute renal failure
- Supportive lab findings:
- Increased resting serum creatine kinase
- No increase in plasma lactate on the forearm exercise test
- Cycle test decrease in heart rate from seven to 15 minutes of stationary cycling
- Rare severe form with rapid progression and onset shortly after birth
Inheritance pattern: Autosomal recessive
What Can Be Learned From This Test
Testing is performed by sequencing the entire coding region of PYGM. This will detect point mutations, small deletions and small insertions. It will not detect a partial or whole gene deletion or duplication. Partial sequencing of exons 1 and 5 can be carried out; please note on submission form if this tiered approach is being requested.
A negative test result does not rule out a genetic cause of myopathy. There are many other genetic forms of myopathy, and this test will only detect mutations associated with glycogen storage disease type V, caused by deficiency of glycogen phosphorylase, muscle form.
Sample Requirements
Draw 2ml鈥4ml of blood in EDTA/purple-top tube (minimum of 1ml鈥2ml for infants).
Turnaround time: 10-14 business days
CPT Codes and Cost
Exon Sequencing (1 & 5 Only)
- Code: 81401
- Cost: $250
Full Gene Sequencing
- Code: 81406
- Cost: $750
Known Variant Testing
- Code: 81479
- Cost: $225