McArdle's disease

McArdle's disease is a type V glycogen storage disease caused by a deficiency of glycogen phosphorylase in muscle.  It is characterised by:

• muscle cramps on exertion
• dark urine due to myoglobin
• absence of normal rise in serum lactate on exertion

Ingestion of sucrose during exercise may help improve symptoms.

References

Baksi, A. et al. Lactate production in McArdle's disease. Postgrad Med J. 1977; 53(617): 161-164.

OMIM. Glycogen storage disease V. Available at http://omim.org/entry/232600