Elevated Serum 1,25-Dihydroxyvitamin D Concentrations in Siblings with Primary Fanconi's Syndrome

THE de Toni–Debré–Fanconi syndrome,^{1 2 3} or Fanconi's syndrome, is characterized by multiple abnormalities in renal tubular function. Defective handling of phosphate, glucose, and amino acids is the cardinal feature of the syndrome.¹² Increased renal clearance of bicarbonate, sodium, potassium, calcium, and uric acid, as well as hyposthenuria, may be present.²³ Rickets, osteomalacia, or both are important clinical manifestations. It has been reported that serum concentrations of 1,25-dihydroxyvitamin D (1,25-(OH)₂D) in Fanconi's syndrome are either decreased^{4 5 6 7} or normal, but inappropriately low relative to the degree of hypophosphatemia.^{6 7 8 9 10 11} We describe two siblings with primary hereditary Fanconi's syndrome, severe bone disease, and.