What will happen during the study?

This is a pilot cross-sectional study that will recruit adults with XLH and matched controls. Collected clinical data to characterize the population and to consider as covariates will include height, length of forearm or tibia, weight, BMI, XLH treatments and their timing, history of fractures, orthopedic surgical history, osteoarthritis, enthesopathy, laboratory biochemistry, and other comorbidities. All participants enrolled in this study will be concurrently enrolled in the FIT core. 

Participants will be seen for a single visit, which is expected to last about four hours. When possible, the research visit can be scheduled to be done on the same day as a routine clinical visit.  See the Study Calendar for timing of assessments.

Informed consent will be obtained at enrollment. To participate in this study, subjects will also need to participate in the Indiana Center for Musculoskeletal Health (ICMH) Function Imaging and Testing (FIT) Core study, because a large portion of the relevant study data are collected as part of the assessments completed during the ICMH FIT Core study. Subjects will sign informed consent for that study testing in addition to this study protocol. As a component of the FIT Core study, participants will undergo bone density testing (DXA), high resolution CT imaging (HR-pQCT), mechanical testing (CBMT), and physical function testing.

Medical history: Review of the subject’s medical history will be collected by the study coordinator using their clinical notes in the electronic health record and by patient report of conditions. This will include clinically relevant diagnoses and surgeries in the past and ongoing conditions. Extensive review of the subject’s bone health will also be collected, including related characteristics and comorbidities and fracture or pseudofracture location and history.

Medications and supplements: all current medications, vitamins, and nutritional supplements will be recorded by the study coordinator on a medication history form. Particular note will be made for the current or prior treatment of XLH with either burosumab or with active vitamin D (calcitriol) and phosphate supplements. For those taking burosumab (typically every 2 weeks or every 4 weeks), the last dose date prior to the study visit will be recorded.

Laboratory test results: While laboratory measurements are not part of the protocol, the most recent relevant clinically conducted measures will be recorded, including serum phosphorus, calcium, creatinine, alkaline phosphatase, PTH and vitamin D. The control subjects will likely not have some or all of these values available.

MRI: Participants will be accompanied the MRI facility, which is an approximately 10-minute walk from the ICMH FIT Core. Upon arrival, they will be screened by the MRI technologist according to standard operating magnetic resonance imaging procedures to ensure safety. In the scanning room, participants will be positioned with the assistance of the MRI technologist and made as comfortable as possible. An MRI coil will be placed over the region of interest. The scan will take approximately 30-60 minutes and will include pulse sequences that allow for the computation of cortical structure and porosity.