Bone mineral density of the spine and radius shaft in children with X-linked hypophosphatemic rickets (XLH).

X-linked hypophosphatemic rickets (XLH) is characterized by inadequate skeletal mineralization. The bone mineral density (BMD) of the radius shaft and the lumbar spine was determined in 13 children with XLH. Ten patients were on treatment, whereas three patients had discontinued treatment 20-32 months prior to this study. Two of them had radiological evidence of rickets. The radius shaft BMD was significantly diminished: Z score was -1.33 +/- 0.89 (P less than 0.001), while the BMD of lumbar spine was significantly augmented (Z score +1.95 +/- 1.17, P less than 0.001). A positive correlation was found between the Z scores for the BMD of the radius shaft and spine. The two patients with overt rickets had lower radius shaft BMD values and a lesser increment of BMD of the spine. The BMD deficit of cortical bone may be related to the lack of efficacy of the treatment and/or to an intrinsic defect of the bone on this disease. On the other hand, the augmented BMD of the lumbar spine might reflect the overabundance of partially mineralized osteoid. The determination of the BMD of the radius shaft by SPA was a sensitive method for detecting abnormalities of the bone mass in XLH patients under treatment without radiological signs of rickets.