A Repeated Study of KRN23 in Adults With X-Linked Hypophosphatemia

Main Inclusion Criteria: 1. 18 years or older 2. Clinical diagnosis of XLH 3. TmP/GFR \< 2.0 mg/dL 4. GFR ≥60 mL/min 5. Corrected Ca \<10.8 mg/dL 6. A willingness to utilize adequate contraception and not become pregnant\[or to have their partner(s) become pregnant\] during the study 7. Additional inclusion criteria apply Main Exclusion Criteria: 1. Have any sign of active infectious disease or have had an infection requiring treatment with antibiotics within 3-weeks of Screening 2. History of known immunodeficiency 3. Pregnant or lactating females subjects or female planning to be become pregnant during the study 4. Receipt of a live (attenuated) vaccine (except for influenza vaccines) within 3-months of Screening, and/or during the study 5. Use of pharmacologic vitamin D metabolite or its analog, phosphate, calcimimetics, and ingestion of aluminum hydroxide antacids within 10-days prior to Screening and/or dosing 6. Use of any supplement containing phosphate, calcium and/or vitamin D within 10-days prior to Screening and/or dosing 7. Condition which could present a concern for either the subject's safety or difficulty with data interpretation 8. Additional exclusion criteria apply