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Amyloidosis is a group of rare diseases that involve abnormal proteins in the body. Amyloidosis is categorized by type. Each type may come with different symptoms, outlooks, and treatment options. If your doctor diagnoses you with amyloidosis, they will also try to determine which type you’re experiencing.
When normal cells make proteins, they fold the proteins in a very specific way. Sometimes, proteins become misfolded and clump together, building up inside different organs. The clumped proteins are called amyloid fibrils or amyloid protein deposits. Different types of proteins can build up in various places in the body, and in distinct quantities, leading to different types of amyloidosis. Most people only have one form of this disease. However, it is rare but possible for someone to have more than one type of amyloidosis at the same time.
Most types of amyloidosis are systemic. This means amyloid deposits occur throughout the body and are found in many kinds of tissue in different locations. The main types of systemic amyloidosis are:
When amyloidosis is localized, this means amyloid proteins are only found in one specific area. Localized amyloidosis may occur in the bladder, airway, eye, or another organ. Localized amyloidosis may have a better prognosis.
AL amyloidosis is also called primary amyloidosis or amyloid light-chain amyloidosis. It is the most common type of amyloidosis in the United States. About 4,500 people are diagnosed with AL amyloidosis in the U.S. each year. AL amyloidosis is more common in men and in people who are at least 50 years old.
This disease affects plasma cells — white blood cells that help fight infection. Plasma cells develop in bone marrow. These cells make antibodies that recognize and fight off germs. Antibodies are proteins made up of multiple pieces, including immunoglobulin light chains and heavy chains. In AL amyloidosis, plasma cells make high levels of abnormal light-chain proteins. These light chains form amyloids — clusters of abnormal proteins that build up in different organs and cause problems.
AL amyloidosis has two subtypes. Two forms of light-chain proteins, known as kappa and lambda, can be responsible for amyloidosis. It may not be important to know which subtype of AL amyloidosis you have, since both types are treated the same way and have similar outlooks.
Your prognosis, or outlook, with AL amyloidosis depends on how early the disease was diagnosed. For about 30 percent of people, this condition isn’t found until the organs are already seriously affected, and people in that situation may only live for a few months. If the disease is discovered earlier, the outlook is likely better. In particular, you may have a better prognosis if amyloidosis doesn’t affect your heart as severely. Your prognosis also depends on how well treatment works. Your doctor can help you understand your own specific outlook.
AA amyloidosis may also be called secondary amyloidosis. Unlike AL amyloidosis, the AA type develops as a response to another underlying disease that causes inflammation. Some illnesses that may lead to AA amyloidosis include:
When these diseases create inflammation, the liver makes a protein called serum amyloid A protein (SAA). When too much of this protein is made over a long period of time, part of the SAA protein can form an amyloid deposit in tissues like the kidney, heart, and liver.
Having an inflammatory disease does not necessarily mean you will get AA amyloidosis. Fewer than 5 percent of people with these conditions develop amyloidosis. AA amyloidosis is the only type that can develop in children, although it more often affects adults.
One study of 374 people with AA amyloidosis found that the median survival period was approximately 11 years after diagnosis. Outcomes have improved in recent years, thanks to newer, more effective treatments. People with better kidney function are more likely to have good outcomes, although many people with this condition will have kidney failure and will require kidney transplants.
Hereditary or familial amyloidosis can be passed down from parent to child. Many different genes can cause this condition, and there are several subtypes of this disease. These subtypes fall under two main groups: ATTR amyloidosis or non-TTR amyloidosis.
Each subtype is caused by a specific gene change. Normally, genes produce proteins that have different jobs within the cell. When a change occurs within a gene, called a mutation, it sometimes leads to proteins with certain abnormalities. In the case of hereditary amyloidosis, a gene mutation leads to a protein that forms an amyloid deposit. These gene mutations are something that you’re born with, but having the gene doesn’t necessarily mean you will develop amyloidosis.
Hereditary ATTR or hATTR amyloidosis is caused by a mutation in a gene that makes the transthyretin (TTR) protein. About 136 different gene changes can cause hATTR amyloidosis, so this disease often looks a little different from one person to the next. However, people within the same family will often have similar symptoms.
Your doctor may want to know exactly which TTR genetic mutation you have, since individual mutations may be likely to affect different organs and require different treatments. This can be done with a sequencing test that “reads” the TTR gene from a blood sample. The most common mutation is called V30M.
People with hereditary ATTR amyloidosis live for an average of seven to 12 years after being diagnosed. However, many factors may affect your outlook, including how early your symptoms started, which gene mutation you have, and which of your organs are affected by amyloid deposits. For this and other types of systemic amyloidosis, you are more likely to have a worse outcome if multiple organs are affected.
Many other gene mutations can also lead to amyloidosis, although these subtypes are all much more rare. Some of the other gene mutations that cause hereditary amyloidosis include:
Each of these genes may also have multiple mutations. For example, scientists currently know of 22 different genetic changes in the apolipoprotein A1 that can cause amyloidosis. It is important for clinicians to figure out which specific genetic change you have before determining the optimal treatment program.
Wild-type ATTR amyloidosis, or ATTRwt amyloidosis, is another type of amyloidosis caused by the TTR protein. Doctors used to call this disease senile systemic amyloidosis or senile cardiac amyloidosis, but these terms are not used anymore.
There are a few key differences between ATTRwt amyloidosis and hereditary ATTR amyloidosis. First, in ATTRwt amyloidosis, the TTR gene is normal and does not contain a mutation, but still produces amyloid. Experts do not yet understand how the normal TTR gene can cause amyloid deposits without any underlying gene mutations. Second, while hereditary ATTR amyloidosis is passed down within families, ATTRwt amyloidosis is not. Instead, it is a disease of aging, most commonly diagnosed in men over age 70.
ATTRwt amyloidosis usually causes heart problems. Because some older men have heart issues caused by other diseases, doctors may not always realize when a person’s heart symptoms are caused by amyloidosis. This means some people may have this condition without realizing it.
People with ATTRwt amyloidosis often have a better outlook than individuals with other types of amyloidosis.
One form of amyloidosis, called dialysis-related or ABM2 amyloidosis, is sometimes experienced by people who have been on kidney dialysis for many years. When someone’s kidneys stop working properly, it becomes harder to filter toxins and wastes out of the body. People with kidney disease may need to undergo a procedure called dialysis, in which a machine filters the blood to remove extra waste. However, dialysis is not always effective at eliminating a protein called beta-2 microglobulin. This protein can prompt amyloid fibrils to build up in your joints and tendons. People with dialysis-related amyloidosis often develop carpal tunnel syndrome and other joint problems.
Usually, only people with severe kidney disease can develop this type of amyloidosis. Dialysis has improved in recent years and is now less likely to cause this disease.
Your doctor can determine your specific type of amyloidosis. You may need to have blood or urine tests before being diagnosed. Additionally, your doctor may perform a biopsy, in which a sample of tissue is removed and studied under a microscope. This can help your doctor determine exactly which protein deposits are collecting in your organs. Your doctor may also use genetic tests to look for certain gene mutations that can cause amyloidosis.
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Todd Gersten, M.D. is a hematologist-oncologist at the Florida Cancer Specialists & Research Institute in Wellington, Florida. Review provided by VeriMed Healthcare Network. Learn more about him here.
Maureen McNulty studied molecular genetics and English at Ohio State University. Learn more about her here.
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