Does the K153R variant of the myostatin gene influence the clinical presentation of women with McArdle disease?

There is individual variability in the clinical manifestation of McArdle disease, with women generally being more severely affected than men. We compared clinical presentation and exercise capacity between (i) four women with McArdle disease (aged 17, 36, 42 and 70 years) who were also carriers of the K153R variant in the myostatin (GDF-8) gene and in (ii) four women with this disorder matched forage (16, 33, 40 and 69 years), lifestyle, and documented genotype modulators of this disease (ACE, AMPD1 and ACTN3), who did not carry the myostatin variant. Except in the youngest patient, clinical severity was higher in K153R carriers than in their K/K(2) controls (aged 33, 40 and 46 years). Peak cardiorespiratory capacity was very low (< or = 13 mLO(2)/kg/min) in all K153R carriers.