Calcium metabolism in the Jansen type of metaphyseal dysplasia

The Jansen type of metaphyseal dysplasia (JMD) is a rare disorder characterized by growth disturbance and progressive metaphyseal changes initially reminiscent of rickets or primary hyperparathyroidism. Seven of the 16 patients described until now presented with hypercalcaemia of unknown origin. We report studies of calcium metabolism in a hypercalcaemic girl with JMD during the first 3 years of life. The patient presented with hypercalcaemia, hypercalciuria, elevated urinary phosphate and cyclic adenosine monophosphate (AMP) excretion as well as increased 1,25-dihydroxyvitamin D concentrations in serum despite suppressed or low normal values of circulating intact parathyroid hormone (PTH) and PTH related peptide (PTHrP). Measurements of biochemical indices of bone turnover indicated increased bone resorption without sufficient compensatory bone formation. The study suggests that the hypercalcaemia in our patient was caused by an unknown factor, which is not PTH or PTHrP, with osteolytic activity and stimulatory effect on the proximal kidney tubule.