Fanconi syndrome is a disorder of the kidney tubes in which certain substances normally absorbed into the bloodstream by the kidneys are released into the urine instead.

De Toni-Fanconi-Debré syndrome

Fanconi syndrome can be caused by faulty genes, or it may result later in life due to kidney damage. Sometimes the cause of Fanconi syndrome is unknown.

Common causes of Fanconi syndrome in children are genetic variations that affect the body's ability to break down certain compounds such as:

• Cystine (cystinosis)
• Fructose (fructose intolerance)
• Galactose (galactosemia)
• Glycogen (glycogen storage disease)

Cystinosis is the most common cause of Fanconi syndrome in children.

Other causes in children include:

• Exposure to heavy metals such as lead, mercury, or cadmium
• Lowe syndrome, a rare genetic disorder of the eyes, brain, and kidneys
• Wilson disease
• Dent disease, a rare genetic disorder of the kidneys

In adults, Fanconi syndrome can be caused by various things that damage the kidneys, including:

• Certain medicines, including azathioprine, cidofovir, gentamicin, and tetracycline
• Kidney transplant
• Light chain deposition disease
• Multiple myeloma
• Primary amyloidosis

Symptoms include:

• Passing large amounts of urine, which can lead to dehydration
• Excessive thirst
• Severe bone pain
• Fractures due to bone weakness
• Muscle weakness

Laboratory tests may show that too much of the following substances may be lost in the urine:

• Amino acids
• Bicarbonate
• Glucose
• Magnesium
• Phosphate
• Potassium
• Sodium
• Uric acid

Loss of these substances can lead to a variety of problems. Further tests and a physical exam may show signs of:

• Dehydration due to excess urination
• Growth failure
• Osteomalacia
• Rickets
• Type 2 renal tubular acidosis

Many different diseases can cause Fanconi syndrome. The underlying cause and its symptoms should be treated as appropriate.

The prognosis depends on the underlying disease.

Contact your health care provider if you have dehydration or muscle weakness.

Bonnardeaux A, Bichet DG. Inherited disorders of the renal tubule. In: Yu ASL, Chertow GM, Luyckx VA, Marsden PA, Skorecki K, Taal MW, eds. Brenner and Rector's The Kidney. 11th ed. Philadelphia, PA: Elsevier; 2020:chap 44.

Chua AN, Kumar R, Foreman JW. Fanconi syndrome and other proximal tubule disorders. In: Johnson RJ, Floege J, Tonelli M, eds. Comprehensive Clinical Nephrology. 7th ed. Philadelphia, PA: Elsevier; 2024:chap 50.