Due to the ultra rare nature of McArdle disease, mistakes have been made in diagnosis .
If patient has an atypical presentation, check whether they have been genetically confirmed.
DNA analysis of the PYGM gene may be undertaken  from blood taken locally.
Over 150 causative mutations identified to date.
There is a significant preponderance of the two most common mutations.
 McArdle Disease: a clinical review. Quinlivan R, Buckley J, James M, et al. J Neurol Neurosurg Psychiatry. doi: 10.1136/jnnp. 2009.195040.
 Intron/exon structure of the human gene for the muscle isozyme of glycogen phosphorylase. Burke J, Hwang P, Anderson L, Lebo R, Gorin F, and Fletterick R. (1987) Proteins 2: 177-187.
McArdle disease is inherited in an autosomal recessive pattern .
General practices are very unlikely to see a second patient, other than possibly a sibling.
Prevalence has been estimated at 1:100,000, based on a carrier frequency of approx. 1:160 [2,3]. In many countries less than half of cases are identified.
The risk of a patient partnering with a carrier and their child having McArdle’s is approx. 1 in 320.
For patients of childbearing age, referral for genetic counseling may be appropriate.
 Online Mendelian Inheritance in Man. http://omim.org/entry/232600
 Treatment of McArdle disease. Haller RG. Arch Neurol 2002; 57:923–4.
 A novel mutation in the PYGM gene in a family with pseudo-dominant transmission of McArdle Disease. Isackson PJ, Tarnopolsky M, and Vladutiu GD (2005) Mol Genet Metab, 85: 239-242.
McArdle Disease Medical Overview