Fanconi Syndrome (also called Fanconi's syndrome) is a disorder in which the proximal tubular function of the kidney is impaired, leading to an decreased reabsorption of electrolytes and nutrients back into the bloodstream. Compounds involved include glucose, uric acid, amino acids, phosphate and bicarbonate.

The diagnosis is based on excessive loss of substances in the urine (eg, glucose, amino acids, phosphate, bicarbonate) in the absence of high plasma concentrations.

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

The most striking clinical feature of Fanconi syndrome is the patient's failure to thrive. Children with Fanconi syndrome typically have a short stature, are frail, have a low muscle tone, and have signs of florid rickets, such as frontal bossing, rosaries, leg bowing, and widening of the wrists, knees, and ankles. Their reflexes may be heightened because of hypocalcemia. Needle-shaped refractile bodies found in the cornea, detectable by slit-lamp examination, are pathognomonic of cystinosis. They are always found in children older than 2 years but may be seen during the first year of life.

There are different diseases known to cause Fanconi syndrome. They can be inherited or congenital as well as acquired. Cystinosis is the most known cause of Fanconi syndrome in children; it is possible, however, to acquire this disease later on in life. Other recognised causes of Fanconi's syndrome are Wilson's disease (a genetically inherited condition of copper metabolism), Lowe Syndrome, Tyrosinemia(Type I), glycogen storage diseases, fructose intolerance, galactosemia, ingesting expired tetracyclines, and as a side effect of tenofovir.