Fanconi Syndrome

Fanconi syndrome is a generalized dysfunction of the PROXIMAL RENAL TUBULE resulting in impaired reabsorption of multiple solutes that were filtered at the glomerulus. Normally, the proximal tubule reabsorbs approximately 65% of filtered sodium and water, nearly 100% of filtered glucose and amino acids, 80% of filtered phosphate, and 80% of filtered bicarbonate. In Fanconi syndrome, damage to proximal tubular transport mechanisms causes these solutes to spill into the urine. The hallmark findings include: (1) GLUCOSURIA with NORMAL blood glucose (glucose appears in the urine because the proximal tubule cannot reabsorb it, NOT because blood glucose is elevated -- this distinguishes it from diabetic glucosuria), (2) AMINOACIDURIA (generalized loss of amino acids into the urine), (3) PHOSPHATURIA causing HYPOPHOSPHATEMIA (phosphate wasting leads to impaired bone mineralization → rickets in children, osteomalacia in adults), (4) BICARBONATURIA causing TYPE 2 (PROXIMAL) RENAL TUBULAR ACIDOSIS (loss of bicarbonate into the urine results in non-anion gap metabolic acidosis with normal anion gap), (5) HYPOKALEMIA from potassium wasting, (6) URICOSURIA causing hypouricemia, and (7) LOW-MOLECULAR-WEIGHT PROTEINURIA (proteins normally reabsorbed by the proximal tubule appear in...