Currently, large oral doses of phosphate and 1,25(OH)2D (calcitriol) are the standard
treatment of patients with familial hypophosphatemic rickets (XLH). While this therapy is
effective in healing the rickets, it is often limited by development of complications due to
the high dose of medications required to achieve cure. Among them are the development of
calcifications in the kidneys and secondary hyperparathyroidism (HPT) which in some patients
may cause complications like high blood calcium level, high blood pressure and damage to the
kidney. A drug to treat secondary hyperparathyroidism was just developed. In a short term
study we found that it might help the treatment of XLH, by allowing the use of lower doses of
the both phosphate and calcitriol. In the present study we will learn if indeed the addition
of this new medicine (Cinacalcet) to the long-term treatment will allow the use of lower
doses of both phosphate and calcitriol and consequently lower the risk of complications.