What Is Thin Basement Membrane Syndrome?
Diffuse weakening of the glomerular basement membrane is the source of the hereditary condition known as thin basement membrane syndrome. It is also called thin basement membrane disease, thin basement membrane nephropathy, or benign familial hematuria. However, the term benign familial hematuria is not used anymore. It is a hereditary disease transmitted in an autosomal dominant pattern.
The glomerulus is made up of thin capillaries and is a part of the filtering unit of the kidney called the nephron. It is a very uncommon disorder diagnosed in less than one percent of the population. When a person has a thin basement membrane condition, their basement membrane thins from 300 to 400 nm in width in healthy individuals to 150–225 nm. Along with IgA (immunoglobulin A) nephropathy, basement membrane syndrome is considered the most common cause of hematuria in adults and children. Most people with thin basement membrane syndrome exhibit normal kidney function throughout their lifetime.
What Is Glomerulus?
The glomerulus is a network of capillaries situated inside the Bowman's capsule. These capillaries are situated between two resistance vessels. The arteriole afferent and the arteriole efferent are the two resistance vessels. Compared to the efferent arteriole, the afferent arteriole has a larger diameter.
The afferent arteriole allows blood to pass into the glomerulus; it then travels via the capillaries and out through the efferent arteriole. This creates a pressure gradient in the capillaries and leads to filtration of the blood, which then finally forms urine.
The capillaries of the glomerulus are not surrounded by interstitial tissue. The proximal layer of the glomerulus is composed of fenestrated endothelium with a diameter of 70 to 100 nm of the individual fenestrae. The distal part of the glomerulus is made up of the glomerular basement membrane, which contains visceral epithelial cells called podocytes.
The glomerular filtration membrane filters water and small solutes and blocks the passage of blood cells and large proteins. The filter formed in the glomerular process is further passed to the rest of the nephron.
The reabsorption process moves the nutrients and water back into the bloodstream. The resulting filtrate from the glomerular filtration membrane consists of essential irons, glucose, smaller proteins, and amino acids. The waste products are excreted into the urine, and the required water and essential ions are again re-absorbed into the bloodstream for further filtration.
What Causes Thin Basement Membrane Syndrome?
Genetic Inheritance - Thin basement membrane syndrome is a disease that is inherited from parents to children. It is a genetic disease caused by the mutation of genes that codes for type 4 collagen. It is an autosomal dominant disease. An autosomal inheritance means one parent containing the gene can transfer the disease to the offspring. If one of the parents has thin basement membrane syndrome, then each child has a 50 % chance of having the disease.
Genetic Mutations - Changes in certain genes that affect the production of type IV collagen are found in affected individuals. The proper structure and operation of the glomeruli's basement membrane depend on the protein type IV collagen. Thin basement membrane syndrome is similar to Alport syndrome, a disease involving a mutation in the type of IV collagen genes. Alport syndrome is a more serious form of thin basement membrane syndrome.
What Are the Symptoms of Thin Basement Membrane Syndrome?
Hematuria - Persistent glomerular bleeding is most commonly found in people with thin basement membrane syndrome, further leading to hematuria. A patient suffering from thin basement membrane syndrome has a family history of hematuria. Blood in the stool is known as hematuria.
Proteinuria: People with the illness are known to have blood levels of protein exceeding 500 mg daily.
High Blood Pressure - Blood pressure is normal, but high blood pressure is also found during clinical examinations.
Less Urine Production - Urine production is hampered due to kidney impairment.
Body Swelling - Swelling in the legs, arms, ankles, and feet is called edema.
Pain - Intermittent flank pain is experienced by patients suffering from the syndrome.
Collagen effect on kidney - Mutations in genes affecting collagen production can lead to Thin Basement Membrane Disease (TBMD), thinning the kidney's basement membrane. This condition primarily causes blood in the urine (hematuria) but usually does not result in severe kidney impairment.
How to Diagnose Thin Basement Membrane Syndrome?
Blood Test: This test measures serum creatinine levels, which are used to determine the glomerular filtration rate.
Urine Test: One can perform a urine test to measure blood pressure, protein levels, and other urinary tract markers.
Kidney Biopsy - A kidney biopsy can be done to check the changes in the glomerular capillaries and blood vessels, which can then be detected on an electron microscope. It is usually done to confirm a diagnosis.
How is Thin Basement Membrane Disease Inherited?
Thin Basement Membrane Disease (TBMD) is typically inherited in an autosomal dominant pattern. This means that only one copy of the altered gene, inherited from one parent, is sufficient to cause the condition. It is associated with mutations in genes that encode collagen, a protein crucial for the structure of the basement membrane in the kidneys.
The basement membrane is a thin, specialized layer that helps filter waste and excess fluids from the blood in the kidneys. When mutations affect the genes responsible for producing collagen in this membrane, it becomes thinner than normal. This thinning can lead to symptoms like blood in the urine (hematuria) and sometimes mild kidney impairment.
How to Treat Thin Basement Membrane Syndrome?
People suffering from thin basement membrane syndrome generally have a good prognosis over a long period of time. They generally live normal lives and are asymptomatic. However, in some patients, complications can arise, requiring medical attention. The treatment modality depends upon the presence and severity of the symptoms. It is generally similar to the symptoms present in chronic kidney disease.
To Lower Blood Pressure - Medications used to lower blood pressure are Angiotensin-converting enzyme inhibitors or Angiotensin II receptor blockers.
To Control Swelling - Diuretic drugs can be prescribed by the physician to control and lower the swelling. Dietary changes should be made by reducing the dietary salt intake.
To Control Frequent Hematuria or Proteinuria or Flank Pain - ACE inhibitors or Angiotensin II receptor blockers can be prescribed.
To Treat Kidney Failure - If there is a worsening of the condition leading to kidney failure, dialysis or a kidney transplant can be done.
Conclusion
Most people with thin basement membrane syndrome do not require treatment as they maintain normal kidney function. Certain symptoms, like hypertension and proteinuria can be treated with medications. Thin basement membrane syndrome is generally asymptomatic and diagnosed when a small amount of blood is found in a urine sample under a microscope. They generally have normal blood pressure and normal kidney function. By decreasing the intraglomerular pressure, angiotensin-converting enzyme inhibitors can reduce pain in the flanks, proteinuria, and regular hematuria.
