ONCOGENIC OSTEOMALACIA - IS THERE A NEW PHOSPHATE REGULATING HORMONE

Oncogenic osteomalacia is a syndrome associated with rare, usually mes enchymal tumours, which is characterized by hypophosphataemia, phospha turia and low concentrations of 1,25-dihydroxyvitamin D. The reversal of clinical and biochemical abnormalities following removal of the tum our, indicates it is the source of a humoral factor that is responsibl e for these abnormalities, It has been demonstrated that the humoral f actor inhibits renal phosphate uptake and reduces I,25-dihydroxyvitami n D production. Although there is evidence that it may act via parathy roid hormone/parathyroid hormone-related peptide receptors and may be a peptide, the factor has not yet been identified, nor has its relatio nship to factors involved in X-linked hypophosphataemic rickets been e stablished. We propose unifying hypotheses for the pathogenesis of onc ogenic osteomalacia and X-linked hypophosphataemic rickets which invol ve defects in the PEX gene. These hypotheses do not fully explain all the available data and it remains possible that hormone(s) with little or no role in X-linked hypophosphataemic rickets may be responsible f or oncogenic osteomalacia.