Amyloidosis is classified into three main forms depending on the cause of the condition. The condition is also referred to as either localized when only one site of the body is affected, or systemic when the disease involves multiple sites of the body. Localized amyloidosis is usually less serious than the systemic forms.
Primary or AL amyloidosis
This is the most common form of amyloidosis. AL amyloidosis accounts for around 80% of cases and is associated with plasma cell dyscrasia or cancer of the plasma cells.
This form of amyloidosis is caused by deposits of immunoglobulin light chain proteins. These proteins are produced by abnormal plasma cells present in the bone marrow and accumulation of the proteins can affect the heart, kidneys, nervous system, and gastrointestinal tract.
Secondary or AA amyloidosis
This form of amyloidosis is most commonly caused by conditions of chronic inflammation such as rheumatoid arthritis or inflammatory bowel syndrome. The protein deposited is the acute phase protein serum amyloid A.
Hereditary or familial amyloidosis
This rare form of amyloidosis is caused by inherited mutations of the genes that code for the transthyretin protein. This protein is mainly produced in the liver.
Depending on the type of amyloidosis a patient has, various organs and tissues in the body may be affected by the disease. Examples of specific parts of the body affected by the different forms of the condition include:
- Kidney – The kidney is commonly affected in primary and secondary amyloidosis but is not usually involved in the familial form of the condition.
- Heart – The heart is affected in the primary and familial form of amyloidosis but rarely by secondary amyloidosis.
- Nervous system – The damage caused to the nervous system can be a significant problem in primary amyloidosis. The nervous system is also affected in a form of familial amyloidosis called Met 30, originally known of as familial amyloid polyneuropathy.
- Liver – The liver is affected in primary and secondary amyloidosis, but rarely in familial amyloidosis.
- Skin and soft tissues – Primary amyloidosis may affect the skin and soft tissues.
- Lungs and vocal cords – Amyloid deposits are often found in the lungs of patients with primary amyloidosis but there may be no symptoms.