What causes amyloidosis

Overview

Amyloidosis is a rare condition characterized by the abnormal buildup of proteins in the body. These proteins, known as amyloid, are misfolded and aggregate into insoluble fibers that deposit in various organs and tissues. This accumulation, called amyloidosis, can disrupt the normal structure and function of these organs, leading to a wide range of symptoms and complications. While the exact cause of amyloidosis varies depending on the type, it fundamentally stems from the body's inability to properly clear or process certain proteins, leading to their abnormal accumulation.

Understanding Amyloid Proteins

Proteins are essential molecules in the body, performing a multitude of functions. They are made up of chains of amino acids, and their specific sequence dictates their three-dimensional shape. This shape is crucial for the protein's function. In amyloidosis, specific proteins undergo a process of misfolding. Instead of maintaining their normal, functional shape, they contort into an abnormal structure. These misfolded proteins are prone to clumping together, forming stable, insoluble deposits known as amyloid fibrils. These fibrils are typically beta-pleated sheets in their structure, which makes them resistant to degradation by the body's natural waste disposal systems.

Types of Amyloidosis and Their Causes

There are many different types of amyloidosis, classified based on the specific protein that forms the amyloid deposits. The most common types and their causes are:

AL Amyloidosis (Light-Chain Amyloidosis)

AL amyloidosis is the most common form of the disease. It arises from abnormal plasma cells in the bone marrow, which are the same cells that produce antibodies. In AL amyloidosis, these plasma cells produce an excess of abnormal light chains (a component of antibodies) that are prone to misfolding and forming amyloid deposits. This type is often associated with conditions like multiple myeloma or other plasma cell disorders. The exact trigger for plasma cells to produce these abnormal light chains is not always understood, but it represents a malfunction in protein production and regulation within these cells.

AA Amyloidosis (Serum Amyloid A Amyloidosis)

AA amyloidosis is caused by chronic inflammatory diseases. In response to long-term inflammation, the liver produces a protein called serum amyloid A (SAA). In individuals with AA amyloidosis, there is an overproduction of SAA, and this protein misfolds and deposits as amyloid in organs, most commonly the kidneys. Conditions that can lead to AA amyloidosis include rheumatoid arthritis, inflammatory bowel disease (Crohn's disease, ulcerative colitis), familial Mediterranean fever, and chronic infections like tuberculosis.

Hereditary Amyloidosis (Transthyretin Amyloidosis - ATTR)

Hereditary amyloidosis is an inherited condition caused by genetic mutations in the TTR gene. This gene provides instructions for making transthyretin, a protein produced mainly by the liver that transports thyroxine (a thyroid hormone) and retinol (vitamin A) in the blood. Certain mutations in the TTR gene lead to the production of abnormal transthyretin protein that misfolds and forms amyloid deposits. These deposits can affect nerves, the heart, and other organs. This form is often referred to as ATTR amyloidosis.

Wild-Type (Senile) ATTR Amyloidosis

This form of ATTR amyloidosis occurs in older individuals and is not caused by a genetic mutation. It is believed to be related to the natural aging process, where the transthyretin protein gradually becomes unstable and misfolds over time, leading to amyloid deposition. It most commonly affects the heart, causing a restrictive cardiomyopathy.

Other Rare Types

Several other less common types of amyloidosis exist, each caused by the misfolding and deposition of different precursor proteins, such as:

• Abeta2M amyloidosis: Associated with long-term kidney dialysis.
• AANF amyloidosis: Involves the atrial natriuretic factor peptide.
• ALECT2 amyloidosis: A rare form linked to mutations in the LECT2 gene.

Factors Contributing to Amyloidosis

While the specific precursor protein and the immediate cause vary, several general factors can contribute to the development of amyloidosis:

• Genetic Predisposition: As seen in hereditary ATTR amyloidosis, inherited gene mutations can significantly increase the risk.
• Chronic Inflammation: Persistent inflammatory conditions can lead to the overproduction of specific proteins like SAA, increasing the risk of AA amyloidosis.
• Age: The risk of certain types, like wild-type ATTR amyloidosis, increases with age.
• Certain Diseases: Conditions such as multiple myeloma, chronic infections, and inflammatory autoimmune diseases are strongly linked to specific types of amyloidosis.
• Immune System Dysregulation: In AL amyloidosis, the malfunctioning of plasma cells represents a form of immune system dysregulation leading to abnormal protein production.

Conclusion

In summary, amyloidosis is fundamentally caused by the misfolding and aggregation of specific proteins into amyloid deposits. The origin of these misfolded proteins can be traced to genetic errors, chronic inflammatory processes, or dysfunctions within specific cell types like plasma cells. Understanding the underlying cause is critical for diagnosis and treatment, as different types of amyloidosis require distinct management strategies.