Fanconi syndrome

Fanconi syndrome (also known as Fanconi's syndrome) is a disease of the proximal renal tubules of the kidney in which glucose, amino acids, uric acid, phosphate and bicarbonate are passed into the urine, instead of being reabsorbed. Fanconi syndrome affects the proximal tubule, which is the first part of the tubule to process fluid after it is filtered through the glomerulus. It may be inherited, or caused by drugs or heavy metals.

Different forms of Fanconi syndrome can affect different functions of the proximal tubule, and result in different complications. The loss of bicarbonate results in Type 2 or proximal renal tubular acidosis. The loss of phosphate results in the bone disease rickets (even with adequate vitamin D and calcium), because phosphate is necessary for bone development.

Eponym
It is named after Guido Fanconi, a Swiss pediatrician; this may be a misnomer since Fanconi himself never identified it as a syndrome; though, as in the case of Goodpasture's syndrome, it is customary to name a syndrome after the first person to note a constellation of symptoms as occurring together.

It should not be confused with Fanconi anemia, a separate disease.

Clinical features
The clinical features of proximal renal tubular acidosis are:
 * Polyuria, polydipsia and dehydration
 * Hypophosphatemic rickets (in children) and osteomalacia (in adults)
 * Growth failure
 * Acidosis
 * Hypokalemia
 * Hyperchloremia

Other features of the generalized proximal tubular dysfunction of the Fanconi syndrome are:
 * Hypophosphatemia/phosphaturia
 * Glycosuria
 * Proteinuria/aminoaciduria
 * Hyperuricosuria

Causes
In contrast to Hartnup disease and related tubular conditions, Fanconi syndrome affects the transport of many different substances, and therefore is not considered to be a defect in a specific channel, but a more general defect in the function of the proximal tubules.

There are different diseases underlying Fanconi syndrome. They can be inherited, congenital or acquired.

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

Other recognised causes of Fanconi's syndrome are Wilson's disease (a genetically inherited condition of copper metabolism), Lowe syndrome, tyrosinemia (Type I), galactosemia, glycogen storage diseases, and fructose intolerance.

Two forms, Dent's disease and Lowe syndrome, are X linked.

Acquired
It is possible to acquire this disease later in life.

Causes include ingesting expired tetracyclines, and as a side effect of tenofovir in cases of preexisting renal impairment. In the HIV population, Fanconi syndrome can develop secondary to use of an antiretroviral regimen containing tenofovir and didanosine. Lead poisoning also leads to Fanconi syndrome.

Monoclonal gammopathy of undetermined significance can also cause the condition.

Multiple myeloma is also a known cause.

Treatment
Treatment of children with Fanconi syndrome mainly consists of replacement of substances lost in the urine (mainly fluid and bicarbonate).