The 577X allele of the ACTN3 gene is associated with improved exercise capacity in women with McArdle’s disease

We assessed the possible association existing between α-actinin-3 (ACTN3) R577X genotypes and the capacity for performing aerobic exercise in McArdle’s patients. Forty adult McArdle’s disease patients and forty healthy, age and gender-matched sedentary controls (21 men, 19 women in both groups) performed a graded test until exhaustion and a constant-load test on a cycle-ergometer to determine clinically relevant indices of exercise capacity as peak oxygen uptake (VO2peak) and the ventilatory threshold (VT). In the group of diseased women, carriers of the X allele had a higher (P < 0.01) VO2peak (15.0 ± 1.2 ml/kg/min) and a higher (P < 0.05) oxygen uptake (VO2) at the VT (11.2 ± 1 ml/kg/min) than R/R homozygotes (VO2peak: 9.6 ± 0.5 ml/kg/min; VO2 at the VT: 8.2 ± 0.7 ml/kg/min). No differences were found in male patients. In women with McArdle’s disease, ACTN3 genotypes might partly explain the large individual variability that exists in the phenotypic manifestation of this disorder.