Rifampin in CYP24A1-related Hypercalcemia and Hypercalciuria

Inclusion Criteria: * Males or females age 6 months to 65 years. * at least one mutations of CYP24A1 * Serum and/or urinary calcium above the normal reference range for age * Serum PTH concentration \<20 pg/ml * Elevated or normal serum concentration of 1,25-dihydroxyvitamin D3. Exclusion Criteria: * Parents/guardians or subjects who, in the opinion of the Investigator, may be non-compliant with study schedules or procedures. * Allergy to rifampin or related medications * Current therapies with medications that have significant drug-drug interactions with rifampin, defined as a medication considered to interact with CYP3A4 or CYP3A5 and either induce or inhibit expression or function of these P450 enzymes. By "drug-drug" interactions we are looking for medications that will affect metabolism or action of rifampin as exclusionary, not medications that will be affected by rifampin. * Pregnancy or breastfeeding * Laboratory abnormalities that indicate clinically significant hepatic, or renal disease: * Aspartate Aminotransferase (AST/SGOT) \> 2.0 times the upper limit of normal Alanine aminotransferase (ALT/SGPT) \> 2.0 times the upper limit of normal Total bilirubin \> 2.0 times the upper limit of normal Creatinine \> 2.0 times the upper limit of normal