By site, patients will be randomized to L-glutamine or placebo in a 1:1 ratio after a 4-week screening period. Patients will undergo 48 weeks of treatment with dosing BID orally, with dose calculated according to patient weight. Patient visits will occur every 4 weeks. After 48 weeks of treatment, dose will be tapered to zero within 3 weeks. A final evaluation visit will occur 2 weeks after last dose.