X-linked hypophosphatemia (XLH) is a rare, inheritable disorder manifesting as
rickets in children and
osteomalacia in adults. While conventional medical treatment with oral
phosphate and
alfacalcidol is recommended in childhood, it is undecided whether adults should continue
therapy. The aim of this 6-year prospective study was to determine the impact of conventional medical treatment on areal bone mineral density (aBMD), bone turnover markers (BTMs) and measures of
calcium homeostasis in 27 adult patients with XLH, 11 of whom received medical treatment. Lumbar spine and total hip aBMD, as assessed by DXA, and biochemical measures of
calcium, phosphate, PTH, 1,25 dihydroxyvitamin D2+3 (1,25(
OH)2D),
fibroblast growth factor 23 (FGF23), P1NP and CTX were measured at baseline and at follow-up. The renal tubular reabsorption of PO4 (TmPO4/GFR) was calculated at both time points. Multilevel mixed-effects linear regression models were used for analyses. During the study period, spine and hip aBMD did not change significantly between treated and non-treated XLH patients. There was a trend towards a decrease in
calcium, phosphate and TmPO4/GFR in the treatment group (p = 0.057, p = 0.080 and p = 0.063, respectively), whereas PTH, FGF23, 1,25(
OH)2D and P1NP did not change significantly in either groups. However, CTX increased significantly in the treated compared to non-treated group (p = 0.044). Continuing conventional medical
therapy in adulthood, although associated with increased
bone resorption, does not promote or prevent loss of bone mass as evidenced from the stable aBMD of the hip and spine in XLH patients.