The pediatric (ages 5 to 12) clinical trial for KRN23 (the antibody developed to control FGF23, which is at least part of the root cause of XLH patient's phosphorus wasting) is about to start.
Details are at clinicaltrials.gov: http://clinicaltrials.gov/ct2/show/NCT02163577?term=krn23&rank=3
Note that while the listing indicates "not yet recruiting," it is NOT too soon to contact the nearest of the locations participating in the study. This is a very limited study, with only thirty participants worldwide, so the slots will be filled quickly.
The XLH Network, Inc. does not endorse or critique specific clinical trials, and does not counsel individual patients either for or against participation in any specific clinical trial. Prospective volunteers should always carefully review the clinical trial's informed consent documentation and protocol, and discuss the pros and cons of their participation with trusted advisors, including their health care providers and family members. The NIH website offers some good questions to consider while deciding whether to enroll in a clinical trial.