Trial Will Test Calcitriol on Bone Health; Now Recruiting in Boston

A Phase 1 trial is enrolling children and adults with X‐linked hypophosphatemia (XLH) to assess the effects of calcitriol, the active form of vitamin D, on kidney function and bone health.

Already underway at Massachusetts General Hospital, in Boston, the trial (NCT03748966) is looking to recruit 20 participants with XLH, ages 6 to 70. For information on enrollment and contacts, please visit the trial’s page here.

Mutations in the gene PHEX, the cause of XLH, lead to low levels of phosphate in the body, a condition called hypophosphatemia. Since phosphate is important for proper bone growth, this can result in rickets-like symptoms, such as bowed legs and short stature.

Currently, the standard treatment for XLH involves a combination of oral phosphate supplements and active vitamin D compounds, such as calcitriol. However, this approach sometimes leads to side effects, including abnormally high levels of calcium in the blood — called hypercalcemia — and the build up of calcium deposits in soft tissues.

Now, the researchers are testing whether calcitriol alone can improve the levels of phosphate and bone mineralization, without the side effects seen with the current standard treatment.

Participants will receive oral calcitriol alone, administered once a day, for one year. The level of calcitriol will be increased during the first three months to optimize the dose.

The study’s main goal is to assess the changes in blood phosphate levels after one year compared with baseline, or the relative to the trial’s start. In addition, the participants’ kidney function will be assessed by measuring phosphate resorption. The amount of calcifications in the kidneys also will be evaluated.

Children will undergo X-rays and special bone CT scans to assess whether calcitriol can reduce rickets’ severity. Growth in children also will be analyzed.

For participants, the trial will require three to five visits to Mass General. Those living in distant locations will have their travel and hotel stays reimbursed. Parking fees also will be covered.

Those who complete the study also will receive two $50 Amazon gift cards.

Eva Liu, MD, from the Harvard Medical School and Brigham and Women’s Hospital, both in Boston, is supervising the study, together with Marie Demay, MD, at the Massachusetts General Hospital.

The Liu lab is focused on understanding the the hormonal and molecular mechanisms that underlie the complications seen in skeletal diseases, such as XLH. In turn, the Demay lab is investigating the role of the vitamin D receptor in bone maintenance.