Safety monitoring during infusion will include: activated clotting times, limb gases, real time monitoring of arterial and venous access pressures, and perfusate temperature. Safety endpoints will be assessed by changes in hematology, serum chemistry, urinalysis, immunologic response to rAAVrh74 and hSGCA, and reported history and observations of symptoms. Efficacy will be measured by the six minute walk test as well as direct muscle testing for strength (MVICT) of lower limb muscles. These quantitative measures will be done at baseline, day 30, 60, 90, 180, and at the end of 1st and 2nd years. Subjects will be evaluated at baseline, infusion visit (days 0-2), and return for follow up visits on days 7, 14, 30, 60, 90, and 180. On Day 180, subjects will undergo a muscle biopsy on the injected muscles in one leg to compare with the pre-treatment biopsy done at baseline screening in the opposite leg to establish the size of muscle fibers and any potential toxicity from gene transfer.