This will be a multi-center, international, open-label, two-period, fixed-sequence crossover study to evaluate the safety and pharmacokinetic effect of single ascending doses of AT2220 on GAA administered 1 hour before initiation of a single alglucosidase alfa infusion. During Period 1 subjects will receive a single intravenous infusion of alglucosidase alfa. During Period 2, each subject will receive one single oral dose of AT2220 one hour prior to initiation of a single alglucosidase alfa infusion.