Two separate evaluations performed at the NIH prior to initiation of therapy will be used as baseline data to compare in a pairwise manner to the change in assessments following treatment with sodium thiosulfate, with all other medications remaining stable. Study treatment will be 16 g/m2 sodium thiosulfate administered 3 times weekly over a period of 10 weeks at the NIH. Subjects who complete 10 weeks of treatment or reach the primary end point by week 6 will be considered completers. Following the treatment period, all participants will return to the NIH for evaluations at weeks 24 and 62.