ESPE Abstracts

Background: X-linked hypophosphatemia (XLH) are rare, inheritable disorders caused by excessive renal phosphate wasting manifesting as rickets in children and osteomalacia in adults. While conventional medical treatment with oral phosphate and alfacalcidol is recommended in childhood, where it heals rickets and rescues some of the growth potential prior to fusion of the growth plates, it is controversial whether adults should continue therapy. There is little evidence for the long-term effect of medical treatment on the adult skeleton.

Objective and hypotheses: The aim of the study was to determine the impact of conventional medical treatment on bone mineral density (BMD) and bone turnover in adult patients with XLH.

Method: DXA scans of the lumbar spine (L2-L4) and total hip BMD were evaluated in 44 adults aged (18+ years) with XLH, 27 of whom were re-examined after six years. Bone formation (N-terminal propeptide of type 1 procollagen, P1NP) and resorption (carboxyterminal cross-linked telopeptide of type 1 collagen, CTX1) markers were analysed in serum samples at baseline (stored at −70° Celcius) and follow-up in one lot. Eleven of the 27 XLH patients had received conventional medical treatment throughout the study period.

Results: The mean change in BMD during the study period was not different between treated and non-treated XLH patients at the lumbar spine (−1.9% vs −0.2%; P=0.55) or hip (−5.2% vs −3.2%; P=0.55). However, bone turnover was higher in the treated compared to non-treated XLH patients as indicated by higher P1NP (+73.7%, P=0.05) and CTX1 (+138%, P=0.04).

Conclusion: Conventional medical treatment for 6 years did not affect the BMD of the hip or spine in XLH adult patients. Although treatment resulted in a state of high bone turnover, bone formation and resorption were balanced, resulting in no net loss of bone mass.