Fanconi syndrome is a condition that affects the proximal renal tubule in the kidney and impairs the organ’s ability to reabsorb substances before they are excreted in the urine.
The proximal tubule processes fluid after it has been filtered through a structure called the glomerulus. In a healthy kidney, the tubule reabsorbs substances such as glucose, uric acid, bicarbonate, phosphate and amino acids. However, in Fanconi syndrome, these molecules are not reabsorbed and are instead passed out of the body in the urine. Fanconi syndrome may occur as an inherited condition or as an acquired illness caused by the ingestion of certain drugs or heavy metals.
Depending on which function of the proximal tubule is affected, Fanconi syndrome causes different types of complications. For example, the loss of bicarbonate in the urine leads to a condition referred to as type 2 or proximal renal tubular acidosis. If phosphate is being lost, the bone disease rickets may develop because this mineral is required for bone development.
Fanconi syndrome is named after the Swiss pediatrician Guido Fanconi who first noted how symptoms of the condition tended to occur together. However, this disease should not be confused with Fanconi anemia, a genetic condition that often leads to leukemia and failure of the bone marrow.
Symptoms of proximal renal tubular acidosis typically include:
- Polyuria or increased frequency of urination
- Polydipsia or increased thirst
- The condition causes hypophosphatemic rickets in children and osteomalacia in adults.
- Failure to thrive
- Low blood potassium (hypokalemia)
- High blood chloride (hyperchloremia)
Symptoms of the generalized proximal renal tubule dysfunction seen in Fanconi syndrome include the following:
- Low blood phosphate (hypophosphatemia)
- Increased urine phosphate (phosphaturia)
- Glucose in the urine (glycosuria)
- Excess serum protein in urine (proteinuria)
- Excess uric acid in the urea (hyperuricosuria)
Cystinosis is the most common genetic condition to cause Fanconi syndrome in children. Other examples include galactosemia, glycogen storage disease, and fructose intolerance. Other causes of the condition in children include heavy metal exposure, Lowe’s disease and Wilson’s disease.
In adults, Fanconi syndrome can be caused by various factors that damage the kidneys such as the use of certain medications (e.g tetracycline, gentamicin, azothioprine), a kidney transplant or the condition multiple myeloma.
Fanconi syndrome is managed by replacing substances in the body that have been excreted in the urine. As Fanconi syndrome can be caused by many different conditions, the underlying cause needs to be established and any symptoms associated with it treated appropriately.
Reviewed by Sally Robertson, BSc