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for people ages 5–12 (full criteria)
at San Francisco, California and other locations
study started
estimated completion:



UX023-CL201 is a randomized, multicenter, open-label, dose finding, Phase 2 study. The study will be conducted in prepubescent children aged 5-12 years with XLH to assess the pharmacodynamics and safety of KRN23 administered via subcutaneous injections monthly (every 4 weeks) or biweekly (every 2 weeks) for a total of 64 weeks. The study consists of a 16-week individual dose Titration Period, followed by a 48-week Treatment Period. The study will enroll approximately 50 pediatric patients with XLH and radiographic evidence of bone disease. Subjects will need to discontinue oral phosphate and vitamin D metabolite therapy prior to randomization and throughout the duration of the study.

Official Title

A Randomized, Open-Label, Dose Finding, Phase 2 Study to Assess the Pharmacodynamics and Safety of the Anti-FGF23 Antibody, KRN23, in Pediatric Patients With X-linked Hypophosphatemia (XLH)


X-linked Hypophosphatemia XLH FGF23 KRN23 Hypophosphatemia Familial Hypophosphatemic Rickets Antibodies


For people ages 5–12


  1. Male or female, aged 5 - 12 years, inclusive, with open growth plates
  2. Tanner stage of 2 or less based on breast and testicular development
  3. Diagnosis of XLH supported by ONE of the following:
  4. Confirmed PHEX mutation in the patient or a directly related family member with appropriate X-linked inheritance
  5. Serum FGF23 level > 30 pg/mL by Kainos assay
  6. Biochemical findings associated with XLH including:
  7. Serum phosphorus ≤ 2.8 mg/dL (0.904 mmol/L)*
  8. Serum creatinine within age-adjusted normal range*
  9. Standing height < 50th percentile for age and gender using local normative data.
  10. Radiographic evidence of active bone disease including rickets in the wrists and/or knees, AND/OR femoral/tibial bowing, OR, for expansion subjects, a RSS score in the knee of at least 1.5 as determined by central read.
  11. Willing to provide access to prior medical records for the collection of historical growth, biochemical and radiographic data, and disease history.
  12. Provide written or verbal assent (if possible) and written informed consent by a legally authorized representative after the nature of the study has been explained,and prior to any research-related procedures.
  13. Must, in the opinion of the investigator, be willing and able to complete all aspects of the study, adhere to the study visit schedule and comply with the assessments.
  14. . Females who have reached menarche must have a negative pregnancy test at Screening and undergo additional pregnancy testing during the study. If sexually active, male and female subjects must be willing to use an acceptable method of contraception for the duration of the study.
  15. Criteria to be determined based on overnight fasting (min. 4 hours) values collected at Screening Visit 2


  1. Use of a pharmacologic vitamin D metabolite or analog (e.g. calcitriol,doxercalciferol, alfacalcidiol, and paricalcitol) within 14 days prior to Screening Visit 2; washout will take place during the Screening Period
  2. Use of oral phosphate within 7 days prior to Screening Visit 2; washout will take place during the Screening Period
  3. Use of calcimimetics, aluminum hydroxide antacids (e.g. Maalox® and Mylanta®),systemic corticosteroids, and thiazides within 7 days prior to Screening Visit 1
  4. Use of growth hormone therapy within 3 months before Screening Visit 1
  5. Use of bisphosphonates for 6 months or more in the 2 years prior to Screening Visit 1
  6. Presence of nephrocalcinosis on renal ultrasound graded ≥ 3 based on the following scale: 0 = Normal 1 = Faint hyperechogenic rim around the medullary pyramids 2 = More intense echogenic rim with echoes faintly filling the entire pyramid 3 = Uniformly intense echoes throughout the pyramid 4 = Stone formation: solitary focus of echoes at the tip of the pyramid
  7. Planned or recommended orthopedic surgery, including staples, 8-plates or osteotomy,within the clinical trial period
  8. Hypocalcemia or hypercalcemia, defined as serum calcium levels outside the age-adjusted normal limits *
  9. Evidence of tertiary hyperparathyroidism as determined by the Investigator
  10. . Use of medication to suppress PTH (e.g. Sensipar®, cinacalcet alcimimetics) within 2 months prior to Screening Visit 1
  11. . Presence or history of any condition that, in the view of the investigator, places the subject at high risk of poor treatment compliance or of not completing the study
  12. . Presence of a concurrent disease or condition that would interfere with study participation or affect safety
  13. . Previously diagnosed with human immunodeficiency virus antibody, hepatitis B surface antigen, and/or hepatitis C antibody
  14. . History of recurrent infection or predisposition to infection, or of known immunodeficiency
  15. . Use of a therapeutic monoclonal antibody within 90 days prior to Screening Visit 1 or history of allergic or anaphylactic reactions to any monoclonal antibody
  16. . Presence or history of any hypersensitivity to KRN23 excipients that, in the judgment of the investigator, places the subject at increased risk for adverse effects
  17. . Use of any investigational product or investigational medical device within 30 days prior to screening, or requirement for any investigational agent prior to completion of all scheduled study assessments
  18. Criteria to be determined based on overnight fasting (min. 4 hours) values collected at Screening Visit 2


  • University of California San Francisco
    San Francisco, California, 94143, United States
  • Shriners Hospital for Children
    Saint Louis, Missouri, 63110, United States
  • Indiana University Hospital
    Indianapolis, Indiana, 46202, United States
  • Yale University School of Medicine
    New Haven, Connecticut, 06520-8064, United States
  • Birmingham Children's University
    Birmingham, B4 6NH, United Kingdom
  • Royal Manchester Hospital
    Greater Manchester, United Kingdom
  • Great Ormond Street Hospital
    London, WC1N3JH, United Kingdom
  • University Medical Center Groningen
    Groningen, 9700RB, Netherlands
  • Bicetre Hospital
    Le Kremlin- Bicetre, 94275, France


in progress, not accepting new patients
Start Date
Completion Date
Ultragenyx Pharmaceutical Inc
Phase 2
Study Type
Last Updated
October 19, 2017