OVERVIEW

What is Fanconi syndrome?

Fanconi syndrome (transliterated as Fàn kě ní zōnɡ hé zhēnɡ) is a kidney disease that affects the proximal renal tubules, impairing their normal reabsorption function. This leads to excessive excretion of useful substances in urine, such as glucose, bicarbonate, phosphate, uric acid, potassium, sodium, and amino acids.

In children, Fanconi syndrome is mostly inherited, while in adults, it is often caused by other conditions, such as chronic interstitial nephritis, Sjögren's syndrome, kidney transplants, or kidney damage from heavy metals (e.g., mercury, lead, cadmium).

Treatment involves addressing the underlying cause and symptomatic management, such as correcting acidosis or supplementing deficient nutrients. Severe cases may require a kidney transplant to save the patient's life.

Is Fanconi syndrome common?

It is rare in China.

However, recent domestic reports of Fanconi syndrome caused by adefovir dipivoxil (a hepatitis B medication) have been increasing.

SYMPTOMS

What are the types of Fanconi syndrome?

Fanconi syndrome can be divided into primary and secondary categories. Primary Fanconi syndrome includes three subtypes: infantile, adult, and idiopathic brush border deficiency types.

What are the manifestations of Fanconi syndrome?

• Infantile Fanconi syndrome: Symptoms usually appear between 6 to 12 months of age, including polyuria, constipation, polydipsia, fatigue, refusal to eat, fever, growth retardation, knock knees, bow legs, etc.

• Adult Fanconi syndrome: The onset is slow, with symptoms typically appearing after 10–20 years of age. Patients exhibit multiple renal tubular dysfunctions, with most showing significant osteomalacia symptoms such as fatigue, soreness in the waist and legs, bone tenderness, and occasional convulsions or numbness. In advanced stages, osteoporosis and bone deformities may occur, with severe cases prone to fractures.

• Idiopathic brush border deficiency Fanconi syndrome: In this type, substances like glucose and amino acids are excessively excreted in the urine, leading to hypokalemia, manifesting as fatigue and arrhythmia. Renal glycosuria may occur, with a high risk of urinary tract infections and stones, presenting as frequent urination, urgency, dysuria, and back pain.

• Secondary Fanconi syndrome: In addition to the above manifestations, symptoms of the underlying primary disease are also present.

What severe complications can Fanconi syndrome cause?

• Bone diseases like osteomalacia can lead to skeletal deformities, affecting daily life and work.

• As the disease progresses, worsening kidney damage may result in renal failure, requiring dialysis or even kidney transplantation.

• Severe primary Fanconi syndrome may lead to death in childhood due to secondary infections or renal failure.

CAUSES

What are the causes of Fanconi syndrome?

Primary Fanconi syndrome is hereditary and mostly begins in infancy, often accompanied by other genetic disorders such as cystinosis, glycogen storage disease type I, galactosemia, hereditary fructose intolerance, cytochrome C oxidase deficiency, Wilson's disease, Lowe syndrome, hereditary osteogenesis imperfecta, and Alport syndrome.

Secondary Fanconi syndrome is caused by damage to renal tubule function due to other diseases. It can result from the following conditions:

• Kidney diseases: such as transplanted kidney, nephrotic syndrome, acute or chronic interstitial nephritis, renal vein thrombosis, Balkan nephropathy, etc.
• Dysproteinemia: such as multiple myeloma, light chain disease, Sjögren's syndrome, amyloidosis, etc.
• Toxicity: such as heavy metals or chemical toxins.
• Drug side effects: such as aristolochic acid, cisplatin, adefovir dipivoxil, etc.
• Others: such as malignant tumors, hyperparathyroidism, and severe hypokalemia, all of which can lead to secondary Fanconi syndrome.

DIAGNOSIS

What tests are needed to diagnose Fanconi syndrome?

The diagnosis is primarily made through urine tests, as Fanconi syndrome presents with glycosuria, phosphaturia, and aminoaciduria.

Additionally, other tests are required to assess disease severity, rule out other conditions, and guide further treatment. These include:

• Hematological tests:
  • Arterial blood gas analysis: To detect acidosis, determine its type, and assess severity.
  • Autoantibodies: Including ANCA, ANA profile, rheumatoid factor, etc., to screen for rheumatic diseases.
  • Blood glucose: To rule out glycosuria caused by diabetes.
  • Electrolytes: To identify electrolyte imbalances.
• Imaging tests:
  • X-ray: If joint pain is present, X-rays of the affected area are needed to check for bone deformities or fractures.
  • Bone density: To assess for osteoporosis.
  • Urinary system ultrasound: To detect kidney stones.

What conditions should Fanconi syndrome be differentiated from?

• Infants: Other causes of renal tubular acidosis, muscle weakness, neurological disorders, primary myopathies, etc.
• Adults: Other metabolic bone diseases, uremia, etc.

TREATMENT

Which department should I visit for Fanconi syndrome?

Nephrology.

How is Fanconi syndrome treated?

Treatment includes addressing the underlying cause and symptomatic management.

• Etiological treatment: Secondary Fanconi syndrome requires active treatment of the primary disease. Only by eliminating the cause can Fanconi syndrome stop worsening or even improve.
  • Wilson's disease or heavy metal poisoning: Promote toxin excretion.
  • Inherited metabolic disorders: Strict dietary control to reduce metabolic toxin accumulation and minimize renal tubular damage.
  • Cystinosis: Low-cystine diet.
  • Bone lesions: Supplement with vitamin D or calcitriol.
• Symptomatic treatment: Tailored to individual conditions, including:
  • Correcting acidosis: Administer alkaline agents as needed; potassium supplementation for hypokalemia.
  • Restoring blood volume: Replenish saline fluids (including sodium, potassium, calcium, etc.).
  • Treating hypophosphatemia: Phosphate supplementation combined with vitamin D.
  • Hypouricemia, aminoaciduria, and proteinuria generally require no treatment.
  • Renal failure: Dialysis or kidney transplantation may be necessary.

Can Fanconi syndrome be cured? Does it require long-term medication?

Primary Fanconi syndrome is often incurable and requires lifelong medication to control symptoms. Effective treatment can prevent worsening kidney and bone damage.

Secondary Fanconi syndrome caused by toxins or drugs may be curable if the cause is identified and eliminated early.

DIET & LIFESTYLE

What should patients with Fanconi syndrome pay attention to in their diet?

• In the early stages of the disease, due to the massive leakage of protein in the renal tubules, a higher intake of high-quality protein, including fish, eggs, and dairy products, is recommended.
• If kidney function has been severely impaired, a low-protein diet should be adopted to avoid worsening kidney damage.
• If edema occurs, sodium intake should be restricted, meaning a low-salt diet, and avoiding pickled foods.
• A low-fat diet is advised, limiting greasy foods and the intake of animal organs.

Does Fanconi syndrome affect fertility?

Because Fanconi syndrome can be caused by certain genetic diseases or co-occur with some hereditary conditions, patients with Fanconi syndrome or those with a family history of the syndrome should seek genetic counseling and prenatal diagnosis before planning a pregnancy to achieve the goal of healthy childbirth.

What should patients with Fanconi syndrome pay attention to in daily life?

If kidney function or bone damage has already occurred, it is important to rest and avoid strenuous exercise.

If osteoporosis is present, falls must be strictly prevented, as fractures can occur easily and heal poorly.

PREVENTION

How to Prevent Fanconi Syndrome?

Patients with primary Fanconi syndrome or those with a family history of the condition should undergo genetic counseling before reproduction to assess the possibility of having healthy offspring. Assisted reproductive technology may be considered if necessary.

For diseases that may lead to secondary Fanconi syndrome, early diagnosis and active treatment can help prevent its occurrence.