OVERVIEW

What is thin basement membrane nephropathy?

Thin basement membrane nephropathy (TBMN), also known as thin basement membrane disease or benign familial hematuria, is a genetic disorder often clustered in families. It is mainly characterized by recurrent microscopic hematuria, usually without obvious symptoms. Diagnosis requires renal biopsy, with the pathological hallmark being diffuse thinning of the glomerular basement membrane. Most patients have a favorable prognosis, generally unaffected in quality of life or lifespan, and do not require specific treatment.

Is thin basement membrane nephropathy common?

Thin basement membrane nephropathy is a rare condition, often familial. Studies suggest its prevalence in the general population may reach 5%–9%, but the diagnosis rate is less than 1%.

How to distinguish between thin basement membrane nephropathy and Alport syndrome?

Thin basement membrane nephropathy and Alport syndrome are distinct diseases, though both are genetic disorders primarily presenting with microscopic hematuria. Alport syndrome is often accompanied by sensorineural hearing loss and ocular abnormalities, with progressive decline in renal function leading to end-stage renal disease and a relatively poorer prognosis. However, some argue that thin basement membrane nephropathy with hematuria and COL4A3 or COL4A4 mutations may essentially represent autosomal dominant Alport syndrome.

SYMPTOMS

What are the common symptoms and clinical manifestations of thin basement membrane nephropathy?

Hematuria, whether microscopic or gross, is relatively common in individuals with a family history, which is why this condition is also referred to as "benign familial hematuria."

• Microscopic hematuria: Manifested as an increase in red blood cells in routine urine tests without gross hematuria. It can be persistent or intermittent, and some cases may be accompanied by mild proteinuria.

• Gross hematuria: When patients have an upper respiratory tract infection, they may experience gross hematuria similar to that seen in glomerulonephritis or IgA nephropathy. Some patients may also experience discomfort such as lower back pain during these episodes.

• Apart from hematuria, patients with thin basement membrane nephropathy generally have normal kidney function and blood pressure. Some may exhibit very mild to moderate proteinuria (usually less than 1.5 g/d), though this occurs relatively infrequently.

How does thin basement membrane nephropathy progress?

Patients with thin basement membrane nephropathy often have no symptoms and are usually diagnosed during routine check-ups. The condition is stable and has a favorable prognosis.

What complications can thin basement membrane nephropathy cause?

Thin basement membrane nephropathy generally does not lead to complications. However, if a patient develops elevated blood pressure, reduced urine output, or increased creatinine levels, it is important to investigate whether other kidney diseases may be present.

CAUSES

What are the common causes of thin basement membrane nephropathy?

Most cases of thin basement membrane nephropathy are autosomal dominant disorders caused by mutations in the COL4A3 or COL4A4 gene regions on chromosome 2. These mutations lead to impaired synthesis of type IV collagen in the kidneys, resulting in incomplete maturation and thinning of the glomerular basement membrane, which manifests as microscopic hematuria. A minority of cases are autosomal recessive or X-linked.

Who is most commonly affected by thin basement membrane nephropathy?

Thin basement membrane nephropathy is relatively rare and tends to occur in individuals with a family history of the condition.

Is thin basement membrane nephropathy contagious?

Thin basement membrane nephropathy is not classified as an infectious disease and cannot be transmitted.

How is thin basement membrane nephropathy inherited?

Thin basement membrane nephropathy is hereditary, typically following an autosomal dominant pattern. This means that the presence of the disease-causing gene will result in the condition.

DIAGNOSIS

How is thin basement membrane nephropathy diagnosed?

When diagnosing thin basement membrane nephropathy, doctors primarily consider microscopic hematuria, family history, absence of renal impairment, and most importantly, renal biopsy pathology results. Only when diffuse thinning of the glomerular basement membrane is observed under electron microscopy can a definitive diagnosis of thin basement membrane nephropathy be made.

What tests are needed to diagnose thin basement membrane nephropathy?

Generally, blood biochemistry, urinalysis, urine red cell morphology, urinary tract ultrasound, and renal biopsy are required. However, for familial isolated microscopic hematuria without proteinuria or only mild proteinuria, no elevated serum creatinine, or no family history of renal failure, a renal biopsy is usually unnecessary.

• Blood biochemistry: Mainly used to assess kidney function.

• Urinalysis: Determines the presence of hematuria, proteinuria, or urinary tract infections.

• Urine red cell morphology: Determines whether hematuria originates from the glomeruli. If not, thin basement membrane nephropathy can be ruled out.

• Urinary tract ultrasound: Evaluates kidney size and structural abnormalities.

• Renal biopsy: Used to obtain kidney pathology results for a definitive diagnosis.

What precautions should be taken for a renal biopsy in thin basement membrane nephropathy?

Before the biopsy, patients should practice breath-holding and urinating while lying down to facilitate cooperation during or after the procedure. After the puncture, absolute bed rest is required for at least 4–6 hours, avoiding movements like turning over or getting out of bed to prevent bleeding risks.

Is a renal biopsy mandatory for diagnosing thin basement membrane nephropathy?

A renal biopsy is an invasive procedure with certain risks and some pain, though most people can tolerate it. While it is the only method to definitively diagnose thin basement membrane nephropathy, not all suspected cases require it. A biopsy is necessary only under the following circumstances to confirm or rule out other kidney diseases:

• 24-hour proteinuria exceeding 1 gram;
• Significantly elevated serum creatinine;
• Oliguria or anuria.

Which diseases are easily confused with thin basement membrane nephropathy? How to differentiate them?

Since thin basement membrane nephropathy primarily manifests as microscopic hematuria, it can be confused with the following conditions:

• IgA nephropathy: May present with microscopic hematuria but usually includes proteinuria. Without treatment, hematuria and proteinuria may worsen, potentially impairing kidney function. Renal pathology shows diffuse IgA deposition along the mesangium.

• Alport syndrome: Also a genetic disorder, accompanied by sensorineural hearing loss and anterior lenticonus. Renal pathology reveals absence of type IV collagen α chains. Genetic testing for COL4A3, COL4A4, and COL4A5 mutations is highly useful in distinguishing it from thin basement membrane nephropathy.

TREATMENT

Which department should I visit for thin basement membrane nephropathy?

It is recommended to see a nephrologist.

Can thin basement membrane nephropathy heal on its own?

Thin basement membrane nephropathy does not resolve spontaneously, but most cases do not require treatment.

How should thin basement membrane nephropathy be treated?

Thin basement membrane nephropathy generally does not require medication and typically does not affect daily life. However, for patients with significant proteinuria (greater than 500–1000 mg/d), especially those with elevated blood pressure and/or elevated serum creatinine or decreased eGFR, angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers are recommended. These may help reduce proteinuria to some extent.

Does thin basement membrane nephropathy require hospitalization?

Hospitalization is necessary only for a kidney biopsy to confirm the diagnosis. Otherwise, it is not required.

Can thin basement membrane nephropathy be cured?

There is currently no cure for thin basement membrane nephropathy, but it does not impair kidney function or quality of life, and treatment is unnecessary.

DIET & LIFESTYLE

What should patients with thin basement membrane nephropathy pay attention to in their diet?

• In terms of diet, focus on eating more fruits and vegetables;

• Maintain a balanced intake of meat and vegetables. If vegetarian, ensure adequate protein by consuming soy products. If milk is tolerated, aim for 300 mL daily to prevent calcium deficiency;

• Avoid relying solely on refined grains; replace part of the staple food with legumes, potatoes, pumpkin, etc.;

• Use less salt and high-sodium seasonings when cooking;

• Limit consumption of pickled vegetables and meats;

• Avoid alcohol as much as possible.

What should patients with thin basement membrane nephropathy pay attention to in daily life?

In daily life, take precautions to avoid colds and overexertion. If hypertensive, manage blood pressure properly. Avoid consuming nephrotoxic foods, medications, or supplements. Engage in about 30 minutes of moderate exercise daily, combining aerobic and strength training. Ensure sufficient sleep and practice self-regulation when facing stress or emotional tension.

Does thin basement membrane nephropathy require follow-up? How?

Patients are advised to undergo blood biochemistry and urinalysis every six months to a year. If symptoms like worsening kidney function, gross hematuria, or significant proteinuria occur, further tests are recommended to rule out other kidney diseases.

Does thin basement membrane nephropathy affect fertility?

It does not affect fertility, but offspring have a high risk of inheriting the condition.

Can patients with thin basement membrane nephropathy fly, engage in intense exercise, or travel to high-altitude areas?

Yes. Patients can fly, perform strenuous activities, and travel to high-altitude regions. Daily life is no different from that of healthy individuals.

PREVENTION

Can thin basement membrane nephropathy be prevented?

Thin basement membrane nephropathy is a genetic disease, and there is currently no way to prevent it.