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for people ages 1–12 (full criteria)
at San Francisco, California and other locations
study started
estimated completion:



UX023-CL301 is a multicenter, randomized, open-label, Phase 3 study comparing the efficacy and safety of KRN23 with active control (oral phosphate/active vitamin D therapy) in children with XLH (aged 1 to ≤12 years) who have radiographic evidence of rickets, open epiphyses, and have received oral phosphate/active vitamin D therapy for ≥ 6-12 consecutive months prior to screening. Approximately 60 subjects will be randomized 1:1 to receive open-label KRN23 administered by subcutaneous injection or oral phosphate and active vitamin D therapy for a total of 64 weeks.

Official Title

A Randomized, Open-Label, Phase 3 Study to Assess the Efficacy and Safety of KRN23 Versus Oral Phosphate and Active Vitamin D Treatment in Pediatric Patients With X Linked Hypophosphatemia (XLH)


X-Linked Hypophosphatemia Hypophosphatemia Familial Hypophosphatemic Rickets Vitamins Vitamin D Ergocalciferols


You can join if…

Open to people ages 1–12

  1. Male or female, aged 1 to ≤12 years with radiographic evidence of rickets as determined by central read
  2. PHEX mutation or variant of uncertain significance in either the patient or in a directly related family member with appropriate X-linked inheritance
  3. Biochemical findings associated with XLH: Serum phosphorus <3.0 mg/dL (0.97 mmol/L)
  4. Serum creatinine within age-adjusted normal range
  5. Serum 25(OH)D above the lower limit of normal (≥16 ng/mL) at the Screening Visit
  6. Have received both oral phosphate and active vitamin D therapy for ≥ 12 consecutive months (for children ≥3 years of age) or ≥ 6 consecutive months (for children <3 years of age) prior to the Screening Visit
  7. Willing to provide access to prior medical records for the collection of historical growth and radiographic data and disease history.
  8. Provide written or verbal assent (as appropriate for the subject and region) 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.
  9. 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.
  10. . 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 highly effective method(s) of contraception for the duration of the study.

You CAN'T join if...

  1. Tanner stage 4 or higher through physical examination
  2. Height percentile >50% based on country-specific norms
  3. Use of aluminum hydroxide antacids (e.g. Maalox® and Mylanta®), systemic corticosteroids, acetazolamide, and thiazides within 7 days prior to the Screening Visit
  4. Current or prior use of leuprorelin (e.g., Lupron®, Viadur®, Eligard®), triptorelin(TRELSTAR®), goserelin (Zoladex®), or other drugs known to delay puberty
  5. Use of growth hormone therapy within 12 months before the Screening Visit
  6. Presence of nephrocalcinosis on renal ultrasound grade 4
  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 hyperparathyroidism (PTH levels 2.5X upper limit of normal [ULN])
  10. . Use of medication to suppress PTH (e.g., cinacalcet, calcimimetics) within 2 months prior to the Screening Visit
  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. . History of recurrent infection or predisposition to infection, or of known immunodeficiency
  14. . Use of a therapeutic monoclonal antibody within 90 days prior to the Screening Visit or history of allergic or anaphylactic reactions to any monoclonal antibody
  15. . 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.
  16. . 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.


  • UCSF
    San Francisco, California, 94158, United States
  • Children's Hospital Los Angeles
    Los Angeles, California, 90027, United States


in progress, not accepting new patients
Start Date
Completion Date
Ultragenyx Pharmaceutical Inc
Phase 3
Study Type
Last Updated
November 2, 2017