Approach to Hypophosphatemic Rickets.

Hypophosphatemic rickets typically presents in infancy or early childhood with skeletal deformities and growth plate abnormalities. The most common causes are genetic (such as X-linked hypophosphatemia), and these typically will result in lifelong hypophosphatemia and osteomalacia. Knowledge of phosphate metabolism, including the effects of fibroblast growth factor 23 (FGF23) (an osteocyte produced hormone that downregulates renal phosphate reabsorption and 1,25-dihydroxyvitamin-D (1,25(OH)2D) production), is critical to determining the underlying genetic or acquired causes of hypophosphatemia and to facilitate appropriate treatment.