Hypophosphatemic osteomalacia: a report of five cases and evaluation of bone markers.

In this study, we analyzed the changes in biochemical markers of bone turnover in five patients with hypophosphatemic osteomalacia. The following bone markers were evaluated: among bone formation markers, total alkaline phosphatase (TAP), bone alkaline phosphatase (BAP), osteocalcin (bone Gla protein, BGP) and procollagen type I N propeptide (PINP); among bone resorption markers, serum beta C-terminal cross-linked telopeptide of type I collagen (s-CTx), urinary hydroxyproline (HYP), and N-terminal and alpha and beta C-terminal cross-linked telopeptides of collagen (NTx and alpha- and beta-CTx). In addition, the alpha/beta-CTx ratio was evaluated. TAP and BAP were the markers with the highest increase in both frequency and magnitude. Conversely, BGP values were low in all patients. Collagen-related markers were slightly increased in nearly half of the patients. Among them, PINP showed the highest proportion of increased values. The alpha/beta-CTx ratio was within normal values in all patients. In conclusion, TAP and BAP seem to be the best bone markers in the diagnostic evaluation of hypophosphatemic osteomalacia. In addition, their high values associated with low levels of BGP provide an even more reliable biochemical profile of this disorder, when associated with the classic mineral and skeletal homeostasis abnormalities.