Participant will complete two 24-hour urine collections for calcium oxalate super-saturation (includes 24-hour urine oxalate excretion) at baseline, inclusive of creatinine determination for assessment of completeness. They will then begin Cystadane anhydrous solution (12 grams/day in subjects younger than 10 years of age, and 20 grams/day in subjects 10 years of age and older, in two divided doses). These doses of betaine have been shown to effectively treat pediatric patients with VB6-resistant homocystinuria and reverse Nonalcoholic Steatohepatitis (NASH) in adult patients, so we expect they will achieve sufficient intra-hepatocyte levels to have an effect in PHI.