Published: 18 Jun 2025

ICD9: 270.0      ICD10: E72.00      ICD11: GB90.42

Fanconi syndrome is a rare disorder that affects the proximal tubules of the kidneys.
These tubules are responsible for reabsorbing essential substances from the filtered fluid in the kidneys back into the bloodstream. In Fanconi syndrome, these tubules malfunction and fail to properly reabsorb these substances.

Think of the kidneys as a complex filtration system. The blood goes through the filter (glomerulus), and essential substances (glucose, amino acids, phosphate, bicarbonate, etc.) are caught in the filtrate. The proximal tubules act like a "recycling center" pulling these valuable resources back into the blood. In Fanconi syndrome, the recycling center is broken, and these essential substances are lost in the urine.

Here's a breakdown of what's happening and what substances are lost:

Location: Proximal tubules of the kidneys.
Problem: Malfunction of the reabsorption process.
Substances Lost in Urine (Key Hallmarks):
Glucose (Glucosuria): Even with normal blood sugar levels.
Amino acids (Aminoaciduria): Building blocks of proteins.
Phosphate (Phosphaturia): Important for bone health and energy.
Bicarbonate (Bicarbonaturia): Helps regulate blood pH.
Potassium (Potassiuria): Essential for nerve and muscle function.
Uric acid (Uricosuria): Waste product from the breakdown of purines.
Water: Contributes to dehydration.
Small proteins (Proteinuria): (often beta-2 microglobulin and other low-molecular-weight proteins)

Causes:

Fanconi syndrome can be either:

Inherited/Genetic (Primary): Often due to mutations in specific genes. Examples include:
Cystinosis (most common inherited cause)
Wilson's disease
Galactosemia
Hereditary tyrosinemia type 1
Lowe syndrome (oculocerebrorenal syndrome)
Acquired/Secondary: Caused by environmental factors or underlying medical conditions. Examples include:
Certain medications (e.g., some antibiotics, chemotherapy drugs, expired tetracycline)
Heavy metal poisoning (e.g., lead, mercury, cadmium)
Multiple myeloma (a type of cancer)
Kidney transplant rejection
Certain autoimmune disorders (e.g., Sjögren's syndrome)

Symptoms:

The symptoms of Fanconi syndrome vary depending on the severity and the specific substances lost. Common symptoms include:

Excessive thirst and urination (polyuria, polydipsia): Due to water loss.
Bone pain and fractures (rickets or osteomalacia): Due to phosphate loss.
Muscle weakness: Due to potassium and other electrolyte imbalances.
Growth retardation (in children): Due to nutrient and electrolyte deficiencies.
Acidosis (metabolic acidosis): Due to bicarbonate loss. This can lead to nausea, vomiting, and lethargy.
Dehydration: Due to excessive fluid loss.
Kidney stones: May develop in some cases.
Fatigue: Due to various electrolyte imbalances and deficiencies.

Diagnosis:

Diagnosis involves:

Urine tests: To detect the presence of glucose, amino acids, phosphate, and other substances that should be reabsorbed.
Blood tests: To check electrolyte levels, kidney function, and blood pH.
Genetic testing: To identify specific gene mutations in inherited cases.
Medical history and physical examination: To identify potential causes and symptoms.

Treatment:

Treatment focuses on managing the symptoms and addressing the underlying cause (if possible). This often involves:

Replacing lost substances: Through oral supplements of phosphate, potassium, bicarbonate, vitamin D, and other nutrients.
Medications: To correct acidosis.
Dietary modifications: To manage electrolyte imbalances.
Treating the underlying cause: If the Fanconi syndrome is secondary to another condition (e.g., removing a toxin, managing multiple myeloma).

Prognosis:

The prognosis depends on the underlying cause and the severity of the condition. With appropriate management, many people with Fanconi syndrome can live relatively normal lives. However, some individuals may experience long-term complications, such as chronic kidney disease.

In summary, Fanconi syndrome is a disorder of the kidney's proximal tubules that leads to the loss of essential substances in the urine, causing a range of health problems. Early diagnosis and treatment are crucial to manage the condition and prevent complications.