Data Safety Monitoring Board will review serum calcium, phosphorus, and urine calcium:creatinine ratio values at the one month visit; if subjects show evidence of hypercalcemia or hyperphosphatemia (serum values > upper limit of normal, age-specific values, see Table 3 below), study drug will be discontinued.(3) If subjects demonstrate evidence of hypercalciuria (urine calcium:cr ratio > 0.6 in 1-2 year olds or > 0.2 in > 2 year olds) study drug will be discontinued.(5) In addition, if 25-hydroxy vitamin D levels > 80 ng/mL are reached, the study drug will be discontinued. In any subject in whom study drug is discontinued, the 3-month laboratory data will still be collected.