What is amyloidosis?
Amyloidosis is the general term given to a relatively rare and serious group of disorders in which an abnormal protein known as amyloid is produced. Amyloid (the word means “starch like”) is an unusually stable material which has a unique chemical structure formed when certain proteins fold in an abnormal way. These protein fibrils progressively deposit and accumulate in organs and tissues of the body, disrupting normal function. Without treatment this may eventually lead to organ damage and failure. At this time it is not known what triggers the initial formation of the amyloid protein and why this happens in such a small proportion of the population.
Amyloidosis can be:
- acquired – occurs spontaneously
- hereditary – occurs due to a faulty gene.
It can also be:
- localised – amyloid protein produced and deposited only in one small area of the body
- systemic – amyloid protein circulates in the blood and deposits in one or several organs of the body.
Amyloidosis is not a cancer but it is equally as serious.
Amyloidosis is classified according to the main protein trigger that causes that particular type of amyloidosis. Each type is given an abbreviation where the first letter A stands for amyloid and the subsequent initials stand for the amyloid protein. For example, in AL amyloidosis the A stands for amyloid and L for the type of fibril protein, light chain. More than 20 different types of amyloidosis have been identified at this time. Many of these are obscure and cause few problems. Each type of amyloidosis is different, requiring different treatments.
Some amyloidosis types include:
AL amyloidosis is a light chain amyloid caused by a bone marrow disorder. AL amyloidosis is caused by an abnormal protein (light chains) made by abnormal plasma cells found in the bone marrow. Plasma cells are part of the body’s immune system. They are responsible for making antibodies, also called immunoglobulins.
In AL amyloidosis a clone or single population of plasma cells grows excessively and produces an abnormal protein called an immunoglobulin light chain. They build up in the bloodstream and are progressively deposited as amyloid fibres (fibrils) in the tissues and organs of the body. AL amyloidosis can involve the kidney, heart, nervous system, liver and gastrointestinal soft tissues. AL amyloidosis is the most commonly diagnosed form of systemic amyloidosis in the western world. Learn more about AL amyloidosis here.
AA amyloidosis occurs when the serum amyloid A (SAA) protein increases substantially in response to a long-term inflammatory disorder. AA amyloidosis used to be known as reactive or secondary amyloidosis, and occurs in patients who have a history of rheumatoid arthritis (children and adults), bronchiectasis, inflammatory bowel disease infections or familial Mediterranean fever, an inherited condition characterised by recurrent episodes of painful inflammation in the abdomen, chest, or joints. The number of people with this type of amyloidosis seems to be declining in the western world with better treatment and control of such inflammatory diseases. The kidney and liver can be affected by this type of amyloidosis.
ATTR (transthyretin gene mutation) and AFib (fibrinogen alpha chain gene mutation) amyloidosis are known as the two main types of hereditary amyloidosis. These types of amyloidosis occur when a gene mutation is inherited leading to the life-long production of an abnormal protein. This amyloid protein deposits in the organs and tissues of the body in the form of an amyloid fibril. Because the protein is not easily broken down it gradually builds up in the organs and tissues of the body disrupting their function. Major organs involved with this type include the heart, nervous system and kidneys. This mutant gene can be passed from one generation to another. Hereditary amyloidosis is known as an autosomal dominant disease, meaning that someone with the mutant gene may have inherited it from their father or mother and they in turn are capable of passing the gene to their children, who each have a 50% chance of inheriting it.
ATTR also includes senile amyloidosis but this is not an inherited disease. It is caused by overproduction of the normal protein TTR. This condition, which mainly affects the heart, is becoming more common as the average age of the population increases. Senile amyloidosis of the heart often coexists with benign bone marrow disorders creating the false impression that AL amyloidosis is the diagnosis.
Over the past 10 years there has been a much greater understanding of these diseases. With earlier diagnosis, great improvements in assessment and treatment regimes, many patients are now experiencing long remissions and living full lives.
How common is amyloidosis?
Amyloidosis is known as a rare group of diseases. In Australia a diagnosis of amyloidosis is not required to be reported on a state or national register, so we have no accurate way of knowing how many people are diagnosed with the disease each year.
Who gets amyloidosis?
Amyloidosis can occur at any age but it is more common in adults over the age of 50. Amyloidosis occurs more frequently in men than in women.
What causes amyloidosis?
At this time it is not known what triggers the initial formation of the amyloid protein and why this happens in such a small proportion of the population. Amyloidosis can be acquired (occurs spontaneously) or hereditary (occurs due to a faulty gene).
Research is going on all the time into possible causes of amyloidosis and certain factors have been identified that mayput some people at an increased risk. These include:
- patients with myeloma may also develop AL amyloidosis (15-20% of myeloma patients)
- patients with a long-term chronic infectious or inflammatory disease are at risk of developing AA amyloidosis
- people who inherit a certain gene mutation may develop hereditary amyloidosis
- patients who require kidney dialysis for a long period of time may be at increased risk of dialysis-associated amyloidosis, although this is rare with modern dialysis techniques.
What are the symptoms of amyloidosis?
Symptoms of amyloidosis depend on which tissues and organs are affected and to what degree. Symptoms vary greatly from patient to patient and between the different types of amyloidosis.
Symptoms are often vague, mimicking other medical conditions. The most common symptoms are:
- unexplained weight loss
- swelling of the ankles and legs due to fluid accumulation.
Other symptoms vary depending on the organ or tissues most affected and may include:
- shortness of breath
- loss of appetite
- enlarged tongue
- unexplained bruising around the eyes
- numbness or tingling in the hands and feet
- lumps in the soft tissue.
Due to the rarity of the disease and vagueness of symptoms, diagnosis may be difficult or delayed. Some of the symptoms described above may also be seen in other illnesses, including viral infections. So, most people with these symptoms don’t have amyloidosis. However, it is important to see your doctor if you have any unusual symptoms, or symptoms that persist much longer than expected so that you can be examined properly.