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 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