Elevated Bone Remodeling Markers of CTX and P1NP in Addition to Sclerostin in Patients with X-linked Hypophosphatemia: A Cross-Sectional Controlled Study

Aspects of bone remodeling have only been scarcely studied in X-linked hypophosphatemia (XLH). In this cross-sectional controlled study, we assessed biochemical indices of bone remodeling and sclerostin in 27 adult patients (median age 47 [range 24-79] years, 19 women, 8 men) with XLH matched with 81 healthy control subjects (1:3) with respect to age-, sex-, and menopausal status. Markers of bone resorption (carboxyterminal cross-linked telopeptide of type 1 collagen, CTX) and formation (N-terminal propeptide of type 1 procollagen, P1NP) were higher in XLH patients compared to controls (median [IQR] 810 [500-1340] vs 485 [265-715] ng/l and 90 [57-136] vs 49 [39-65] ug/l, respectively, both p < 0.001) as well as sclerostin (0.81 [0.60-1.18] vs 0.54 [0.45-0.69] ng/ml, p < 0.001). Similar differences were found when comparing currently treated (with phosphate and alfacalcidol) (n = 11) and untreated (n = 16) XLH patients with their respective controls. We found no significant associations with treatment status and indices of bone remodeling or sclerostin although sclerostin tended to be increased in untreated versus treated (p = 0.06). In contrast to previous histomorphometric studies suggesting a low remodeling activity in XLH, these biochemical indices suggest high osteoblast and osteoclast activity. Further studies are needed to ascertain if the higher sclerostin level in XLH is related to osteocyte dysfunction or represents a secondary phenomenon.