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Fanconi Syndrome

By

L. Aimee Hechanova

, MD, Texas Tech University Health Sciences Center, El Paso

Last full review/revision Jul 2020| Content last modified Jul 2020
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Fanconi syndrome consists of multiple defects in renal proximal tubular reabsorption Introduction to Renal Transport Abnormalities Many substances are secreted or reabsorbed in the renal tubule system, including electrolytes, protons, bicarbonate molecules, glucose, uric acid, amino acids, and free water. Dysfunction of... read more , causing glucosuria, phosphaturia, generalized aminoaciduria, and bicarbonate wasting. It may be hereditary or acquired. Symptoms in children are failure to thrive, growth retardation, and rickets. Symptoms in adults are osteomalacia and muscle weakness. Diagnosis is by showing glucosuria, phosphaturia, and aminoaciduria. Treatment is sometimes bicarbonate and potassium replacement, removal of offending nephrotoxins, and measures directed at renal failure.

Etiology of Fanconi Syndrome

Fanconi syndrome can be

  • Hereditary

  • Acquired

Hereditary Fanconi syndrome

This disorder usually accompanies another genetic disorder, particularly cystinosis. Cystinosis is an inherited (autosomal recessive) metabolic disorder in which cystine accumulates within cells and tissues (and is not excreted to excess in the urine as occurs in cystinuria Cystinuria Cystinuria is an inherited defect of the renal tubules in which reabsorption of cystine (the homodimer of the amino acid cysteine) is impaired, urinary excretion is increased, and cystine stones... read more ). Besides renal tubular dysfunction, other complications of cystinosis include eye disorders, hepatomegaly, hypothyroidism, and other manifestations.

Acquired Fanconi syndrome

Pathophysiology of Fanconi Syndrome

Various defects of proximal tubular transport function occur, including impaired resorption of glucose, phosphate, amino acids, bicarbonate, uric acid, water, potassium, and sodium. The aminoaciduria is generalized, and, unlike that in cystinuria, increased cystine excretion is a minor component. The basic pathophysiologic abnormality is unknown but may involve a mitochondrial disturbance. Low levels of serum phosphate cause rickets, which is worsened by decreased proximal tubular conversion of vitamin D to its active form.

Symptoms and Signs of Fanconi Syndrome

In hereditary Fanconi syndrome, the chief clinical features—proximal tubular acidosis, hypophosphatemic rickets, hypokalemia, polyuria, and polydipsia—usually appear in infancy.

When Fanconi syndrome occurs because of cystinosis, failure to thrive and growth retardation are common. The retinas show patchy depigmentation. Interstitial nephritis Tubulointerstitial Nephritis Tubulointerstitial nephritis is primary injury to renal tubules and interstitium resulting in decreased renal function. The acute form is most often due to allergic drug reactions or to infections... read more Tubulointerstitial Nephritis develops, leading to progressive renal failure that may be fatal before adolescence.

In acquired Fanconi syndrome, adults present with the laboratory abnormalities of renal tubular acidosis (proximal type 2—see Table: Some Features of Different Types of Renal Tubular Acidosis* Some Features of Different Types of Renal Tubular Acidosis* Renal tubular acidosis (RTA) is acidosis and electrolyte disturbances due to impaired renal hydrogen ion excretion (type 1), impaired bicarbonate resorption (type 2), or abnormal aldosterone... read more ), hypophosphatemia, and hypokalemia. They may present with symptoms of bone disease (osteomalacia) and muscle weakness.

Diagnosis of Fanconi Syndrome

  • Urine testing for glucose, phosphates, and amino acids

Diagnosis is made by showing the abnormalities of renal function, particularly glucosuria (in the presence of normal serum glucose), phosphaturia, and aminoaciduria. In cystinosis, slit-lamp examination may show cystine crystals in the cornea.

Treatment of Fanconi Syndrome

  • Sometimes sodium bicarbonate or potassium bicarbonate or sodium citrate or potassium citrate

  • Sometimes potassium supplementation

Other than removing the offending nephrotoxin, there is no specific treatment.

Acidosis may be lessened by giving tablets or solutions of sodium bicarbonate or potassium bicarbonate or sodium citrate or potassium citrate, eg, Shohl’s solution (sodium citrate and citric acid; 1 mL is equivalent to 1 mEq or 1 mmol of bicarbonate) given 1 mEq/kg (1 mmol/L) bid to tid or 5 to 15 mL after meals and at bedtime.

Potassium depletion may require replacement therapy with a potassium-containing salt.

Kidney transplantation Kidney Transplantation Kidney transplantation is the most common type of solid organ transplantation. (See also Overview of Transplantation.) The primary indication for kidney transplantation is End-stage renal failure... read more has been successful in treating renal failure. However, when cystinosis is the underlying disease, progressive damage may continue in other organs and eventually result in death.

Key Points

  • Multiple defects impair proximal tubular reabsorption of glucose, phosphate, amino acids, bicarbonate, uric acid, water, potassium, and sodium.

  • Fanconi syndrome is usually caused by a drug or accompanies another genetic disorder.

  • In hereditary Fanconi syndrome, proximal tubular acidosis, hypophosphatemic rickets, hypokalemia, polyuria, and polydipsia usually appear in infancy.

  • Test urine for glucosuria (particularly in the presence of normal serum glucose), phosphaturia, and aminoaciduria.

  • Treat by giving combinations as needed of potassium or sodium with either bicarbonate or citrate, or sometimes with just a supplemental potassium salt.

Drugs Mentioned In This Article

Drug Name Select Trade
No US brand name
ZANOSAR
ACHROMYCIN V
VIDEX
IFEX
VISTIDE
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