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Fanconi Syndrome - Etiology, Pathophysiology, Symptoms, Diagnosis and Treatment.

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Fanconi syndrome is characterized by a defect in the proximal tubules of the kidney. To know more about this condition, read the following article.

Medically reviewed by

Dr. Manzoor Ahmad Parry

Published At October 19, 2022
Reviewed AtAugust 10, 2023

What Is Fanconi Syndrome?

Fanconi syndrome is named after Swiss pediatrician Guido Fanconi. It is characterized by the defect in the proximal tubules of the kidney resulting in malabsorption of the electrolytes and various substances which are normally absorbed by the proximal tubules. It includes amino acids, bicarbonate, glucose, phosphate, proteins, and uric acid.

What Is the Difference Between Fanconi Syndrome And Fanconi Anemia?

Fanconi syndrome is a defect in the proximal tubules of the kidney, whereas Fanconi anemia is a rare disorder affecting the bone marrow resulting in decreased secretion of all types of blood cells.

What Is the Normal Function of Proximal Tubules of the Kidney?

Proximal convoluted tubules are the major components of the kidney. Their function includes:

  • Reabsorption of the majority of electrolytes and substances from the glomerular ultrafiltrate.

  • It regulates acid-base balance.

  • It regulates fluid-electrolyte balance.

What Is the Etiology of Fanconi Syndrome?

The etiology could be either due to acquired or inherited causes.

Inherited Causes:

  • Cystinosis - It is characterized by the accumulation of amino acids called cysteine within the cells of the body.

  • Galactosemia - It is a condition characterized by a defect in the processing of simple sugar called galactose.

  • Glycogenosis - It is a group of genetic disorders characterized by the defect in the usage and storage of glycogen in the body.

  • Dent Disease - It is characterized by damage to the proximal tubules of the kidney, causing chronic kidney disease.

  • Hereditary Fructose Intolerance - It is characterized by the genetic defect in the enzyme required for the breakdown of fructose.

  • Wilson’s Disease - It is characterized by the accumulation of copper in the organs of the body.

  • Lowe Syndrome - It is a rare disorder characterized by defects in the eyes, kidneys, brain, etc.

  • Mitochondrial Cytopathies - These are a group of multisystem disorders affecting the muscles and the nerves primarily.

Acquired Causes:

  • Antiviral Drugs - Nucleoside reverse transcriptase inhibitors (NRTIs) may cause defects in the reabsorption of proximal tubules.

  • Chemotherapeutic Agents - Cisplatin is found to be involved in causing Fanconi syndrome.

  • Antibiotics - Gentamicin is reported to be involved in Fanconi syndrome.

  • Immunosuppressive Drugs - Azathioprine is reported to be causing Fanconi syndrome.

  • Monoclonal Gammopathy - It is characterized by the presence of abnormal monoclonal proteins in the blood.

  • Lead poisoning - It is repeated to be one of the causes of Fanconi syndrome.

What Is the Pathophysiology of Fanconi Syndrome?

The above said etiologies would result in Fanconi syndrome by the following mechanisms:

  • The decreased influx of solute into the blood from the tubular epithelium.

  • Increased back flux of solute from the cells that separate the tubular epithelium and the blood to the glomerular filtrate.

  • The altered tubular permeability can cause malabsorption of the tubules.

  • Any problem with the transport carriers would result in malabsorption of the electrolytes and thereby resulting in Fanconi syndrome.

  • All this would result in renal tubular acidosis as the reabsorption of bicarbonates is affected in Fanconi syndrome.

What Are the Symptoms of Fanconi Syndrome?

The symptoms include:

  • Fatigue.

  • Weakness.

  • Polyuria (increased urination).

  • Polydipsia (excessive thirst).

  • Dehydration.

  • Paresthesia.

  • Tremor.

  • Muscle weakness.

  • Acidosis.

  • Hypokalemia (decreased serum potassium).

  • Bone pain.

  • Bone deformity.

  • Osteomalacia (softened bones).

  • Hypophosphatemic rickets (bone defect arising as a result of decreased phosphate levels).

  • Glycosuria (excess sugar in the urine).

  • Growth failure.

  • Proteinuria (presence of protein in the urine).

  • Hyperuricosuria (increased excretion of urate in the urine).

What Is the Differential Diagnosis of Fanconi Syndrome?

  • Diabetes Mellitus And Diabetes Insipidus - As polydipsia and polyuria are the common signs of this condition, which are also seen in Fanconi syndrome. Hence, this should be noted while considering the diagnosis.

How Is Fanconi Syndrome Diagnosed?

The steps in diagnosis include:

1. Medical and Family History: A thorough medical and family history of the patient is important as it plays a vital role in diagnosing the cause of the condition and provides details about the presence of pre-existing genetic diseases, Wilson's disease, lower syndrome, etc. Patients should be enquired about the use of the above-discussed drugs under the etiology of Fanconi syndrome. This would help in the effective management of the condition.

2. Clinical Examination: Clinical examination would help to check for the signs of the condition as well as the underlying diseases such as bone deformities, growth retardation, and other neuromuscular symptoms associated with the disease.

3. Blood Test:

  • Serum Bicarbonate Levels - This would indicate the reduced serum bicarbonate levels. In the case of renal tubular acidosis occurring due to Fanconi syndrome, the bicarbonate levels are altered in different types in type 1 - 10 to 20 mEq/L, type 2 - 12 to 18 mEq/L, type 4 - greater than 17 mEq/L.

  • Serum Chloride Levels - This would indicate increased chloride concentration.

  • Serum Phosphate Levels - This would indicate decreased serum phosphorus.

  • Blood pH - This would reveal the decreased pH indicating metabolic acidosis.

  • Serum Potassium Levels - It is low in types 1, 2, and 3 and high in type 4.

  • Blood Urea Nitrogen and Creatinine Levels - Shows normal levels, indicating normal renal function.

4. Urine Test:

  • Urinary Retinol Binding Protein 4 - It is the most sensitive marker to detect the loss of proximal tubular function.

  • Urinary Lactate - This would indicate increased urinary lactate levels.

  • Urinary pH - In type 1, the pH is greater than 5.5, and in types 2 and 4, it shows a pH of less than 5.5.

5. Acid Load Test: This test is mainly used in the diagnosis of renal tubular acidosis caused due to Fanconi syndrome. This acid is infused into the blood with 100 mg/kg of ammonium chloride, and the pH of the urine and plasma bicarbonate levels should be monitored once in three hours. In healthy individuals, the infused acid will get excreted completely with restored normal urine pH. In the case of patients with type 1 RTA, the urine pH will be greater than 5.5.

6. Bicarbonate Infusion Test: Bicarbonate is infused into the blood, and the fractional excretion of bicarbonate is measured. In the case of patients with type 2 RTA, the urine pH increases because of the presence of excessive bicarbonate in the urine.

How Is Fanconi Syndrome Treated?

The main goal of the treatment is to replace the lost substances in the urine. The methods in treatment include:

  • Stop the Offending Drug - If the patient is found to be taking any of the drugs serving as an etiology of Fanconi syndrome. It should be stopped immediately.

  • Treat Metal Poisoning - If metal poisoning is found to be the cause, it should be treated to prevent further loss of electrolytes in the urine.

  • Replacement of Lost Electrolytes - The lost electrolytes in the urine should be replaced, including bicarbonate, potassium, and phosphate.

  • Treat the Underlying Cause - The underlying syndrome or the cause of Fanconi syndrome should be treated to cure the condition effectively.

Conclusion:

Fanconi syndrome occurs due to the malabsorption of electrolytes in the proximal tubules of the kidney. The electrolytes lost in the urine should be replaced once it is diagnosed, as the electrolytic loss would affect the normal homeostasis of the body. It is better to consult a nephrologist for the proper management of Fanconi syndrome. The patients should be monitored for serum electrolyte levels and the urinary loss of electrolytes after treatment.

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Dr. Manzoor Ahmad Parry
Dr. Manzoor Ahmad Parry

Nephrology

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