Fanconi Syndrome

Key points

• Fanconi syndrome is a generalised proximal renal tubular reabsorptive disorder causing urinary loss of multiple solutes.
• Type 2 (proximal) renal tubular acidosis can occur because proximal bicarbonate reabsorption is impaired.
• Aminoaciduria is a typical feature, together with urinary wasting of phosphate, glucose despite normal blood glucose, urate and low-molecular-weight proteins.
• Osteomalacia/rickets can result from chronic phosphate wasting; important causes include inherited disorders and acquired drug/toxin injury.
• Cystinosis is a classic inherited cause of Fanconi syndrome in children; other causes include Lowe syndrome, hereditary fructose intolerance, tyrosinaemia, Wilson disease, ifosfamide and tenofovir.
• MRCP discriminator: normal blood glucose + glycosuria + phosphate wasting + aminoaciduria ± proximal RTA → Fanconi syndrome.
• Exam trap: Fanconi syndrome is a generalised proximal tubular wasting disorder; isolated proximal RTA alone is not Fanconi syndrome.