What is amyloidosis?
Amyloidosis is a group of diseases that are a consequence of abnormal protein deposits in various tissues of the body. These abnormal proteins are called amyloid. Depending on the structure of the particular amyloid, the protein can accumulate in an isolated tissue or be widespread, affecting numerous organs and tissues. There are over 30 different amyloid proteins. Each amyloid protein is arranged in a structure called a fibril. Fibrils are low molecular weight proteins that are derived from precursor proteins. Fibrils of amyloid can float in the plasma of blood and deposit into tissues of the body.
Amyloid protein can be deposited in a localized area and may not be harmful or only affect a single tissue of the body impairing its function. This form of amyloidosis is called localized amyloidosis. Amyloidosis that affects many tissues throughout the body is referred to as systemic amyloidosis. The systemic form can cause serious changes in virtually any organ of the body, including the kidneys, heart (cardiac amyloidosis), and lungs.
Systemic amyloidosis has been classified into three major types that are very different from each other. These are distinguished by a two-letter code that begins with an A (for amyloid). The second letter of the code stands for the protein that accumulates in the tissues in that particular type of amyloidosis. The major types of systemic amyloidosis are currently categorized as primary (AL), secondary (AA), and hereditary (ATTR, amyloid apolipoprotein A1 or AApoAI, amyloid apolipoprotein A2 or AApoAII, AGel, ALys, AFib).
Amyloidosis that occurs as its own entity is called primary amyloidosis. Secondary amyloidosis is amyloidosis that occurs as a byproduct of another illness, including chronic infections (such as tuberculosis or osteomyelitis), or chronic inflammatory diseases (such as rheumatoid arthritis, ankylosing spondylitis, and inflammatory bowel disease). Other forms of amyloidosis include beta-2 microglobulin amyloidosis from chronic kidney dialysis and localized amyloidoses. Amyloidosis that is localized to a specific body area from aging does not have systemic implications for the rest of the body. The protein that deposits in the brain of patients with Alzheimer's disease is a form of amyloid.
Immunoglobulin light chain (AL) amyloidosis or primary amyloidosis
Primary amyloidosis, or AL, occurs when a specialized cell in the bone marrow (plasma cell) spontaneously overproduces a particular protein portion of an antibody called the light chain. (This is why the primary form is coded as AL.) The deposits in the tissues of people with primary amyloidosis are AL proteins. It can affect the heart, kidney, liver, and skin. This is the most common type of amyloidosis. Primary amyloidosis can occur with a bone marrow cancer of plasma cells called multiple myeloma (fewer than 20% of AL patients). Primary amyloid, including multiple myeloma cancer, is not associated with any other diseases but is a disease entity of its own, conventionally requiring chemotherapy treatment. Researchers at the Mayo Clinic in Rochester, Minn., and Boston University in Boston, Mass., have demonstrated the benefits of stem-cell transplantation therapy for primary amyloidosis. In stem-cell transplantation, the patients' own stem cells are harvested to treat primary amyloidosis by replacing abnormal plasma cells in the bone marrow.
AA amyloidosis (secondary amyloidosis)
When amyloidosis occurs secondarily as a result of another illness, such as chronic infections (for example, tuberculosis or osteomyelitis) or chronic inflammatory diseases (for example, rheumatoid arthritis and ankylosing spondylitis), the condition is referred to as secondary amyloidosis or AA amyloidosis. The amyloid tissue deposits in secondary amyloidosis are AA proteins. The treatment of patients' AA amyloidosis is directed at treating the underlying illness in that particular patient.
Familial amyloidosis (hereditary amyloidosis)
Familial amyloidosis (ATTR, AApoAI, AApoAII, AGel, ALys, AFib) is a rare form of inherited amyloidosis. It is more common in African-Americans. The amyloid deposits in most familial amyloidosis are composed of the protein transthyretin, or TTR, which is made in the liver. Familial amyloidosis is an inherited autosomal dominant in genetics terminology. This means that for the offspring of a person with the condition, there is a 50% chance of inheriting it. This form of amyloidosis is also referred to as hereditary amyloidosis. This type of amyloidosis can affect the nerves and the heart.
Beta-2 microglobulin amyloidosis (dialysis amyloidosis)
Beta-2 microglobulin amyloidosis occurs when amyloid deposits develop in patients on dialysis with longstanding kidney failure. The amyloid deposits are composed of beta-2 microglobulin protein and are often found around joints.
The many forms of localized amyloidosis are a result of amyloid deposits in specific areas of the body and are distinct from systemic forms of amyloidosis that deposit amyloid throughout the body. Localized amyloid deposits occur in the brain from Alzheimer's disease. In various tissues, often with aging (senile amyloidosis), amyloid can be locally produced and deposited to cause tissue injury. Prions are infectious amyloid proteins that transmit the diseases kuru, Creutzfeldt-Jakob disease, fatal familial insomnia, and Gerstmann-Straussler-Scheinker syndrome.