(See also Introduction to Disorders of Kidney Tubules.)
Fanconi syndrome is a rare disorder of kidney tubule function that results in excess amounts of glucose, bicarbonate, phosphates (phosphorus salts), uric acid, potassium, and certain amino acids being excreted in the urine.
Fanconi syndrome is unrelated to—and should not be confused with—Fanconi anemia.
Fanconi syndrome may be hereditary or may be caused by
Fanconi syndrome usually occurs with another hereditary disorder, such as cystinosis. Cystinosis is an inherited disorder of amino acid metabolism characterized by abnormal deposits of the amino acid cystine throughout the body and abnormal concentrations of cystine in the urine. Abnormal cystine deposits cause eye disorders, an enlarged liver, and an underactive thyroid gland.
In hereditary Fanconi syndrome, symptoms of excessive drinking and excessive urination usually begin during infancy.
In adults, symptoms may not develop until the disorder has been present for some time. The most common symptoms in adults include weakness and bone pain.
Most often, some damage to bones or kidney tissue has occurred before the diagnosis is made.
The symptoms and a test that shows abnormalities in the blood (such as a high level of acid) or urine (such as a high level of glucose) may lead a doctor to suspect Fanconi syndrome. The diagnosis is confirmed when high levels of glucose (despite a normal blood glucose), phosphates, and amino acids are detected in the urine.
Fanconi syndrome cannot be cured, but it can be controlled with proper treatment. Effective treatment can keep the damage to bones and kidney tissue from getting worse and in some cases correct it. The high acid level of the blood (acidosis) may be neutralized by drinking sodium bicarbonate. People with low potassium levels in the blood may need to take potassium supplements by mouth.
Bone disease requires treatment with phosphates and vitamin D supplements given by mouth.
Kidney transplantation may be lifesaving if a child with the disorder develops kidney failure, but if cystinosis is the underlying disease, progressive damage may continue in other organs and eventually result in death.