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