Fanconi syndrome is listed among the populations at risk for which electrolyte disorder?

• A. Hyperkalemia
• B. Hypophosphatemia
• C. Hyperphosphatemia
• D. Hypomagnesemia

Answer: (B)

Fanconi syndrome causes generalized dysfunction of the proximal tubule, which leads to wasting of filtered phosphate in the urine. The proximal tubule is responsible for reclaiming most of the phosphate via sodium-phosphate cotransporters; when this area is damaged, phosphate reabsorption drops and phosphaturia increases, pulling serum phosphate down and causing hypophosphatemia. This is the classic electrolyte abnormality associated with Fanconi syndrome, and it can contribute to bone problems like osteomalacia or rickets due to impaired mineralization. While other disturbances such as occasional magnesium loss can occur with proximal tubule dysfunction, hypophosphatemia best fits the pattern seen in Fanconi syndrome.