Amyloidosis
Medical Author: William C. Shiel Jr., MD, FACP, FACR
What is amyloidosis?
Amyloidosis is a group of diseases that result from the abnormal
deposition of a
particular protein, called amyloid, in various 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. This form of amyloidosis is called localized amyloidosis. Amyloidosis that affects tissues throughout the body is referred to as systemic amyloidosis. Systemic amyloidosis can cause serious changes in virtually any organ of the
body.
Amyloidosis can occur as its own entity or "secondarily" as a result of
another
illness, including multiple myeloma, chronic infections (such as
tuberculosis or osteomyelitis), or chronic inflammatory
diseases (such as
rheumatoid arthritis and ankylosing spondylitis). Amyloidosis can also be localized to a specific body area from aging. This localized form of amyloidosis 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.
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 types of systemic amyloidosis are currently categorized as primary (AL), secondary (AA), and hereditary
(ATTR).
In addition, other forms of amyloidosis include beta-2 microglobulin amyloidosis and localized amyloidoses.
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 it is coded as AL.) The deposits in the tissues of
people with primary amyloidosis are AL proteins. Primary amyloidosis can occur with a bone marrow cancer of plasma cells called multiple myeloma. Primary amyloid 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, Minnesota, and Boston University in Boston, Massachusetts, have demonstrated benefits from stem-cell transplantation, harvesting patients' own stem cells to treat primary amyloidosis.
Secondary amyloidosis
When amyloidosis occurs
"secondarily" as a result of another illness, such as multiple myeloma, 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. The amyloid tissue deposits in secondary amyloidosis are AA proteins. The treatment of patients' secondary amyloidosis is directed at treating the underlying illness in that particular patient.
Familial amyloidosis
Familial amyloidosis, or ATTR, is a rare form of inherited amyloidosis. The amyloid deposits in 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.
Beta-2 microglobulin 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.
Localized amyloidoses
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, amyloid can be locally produced and deposited to cause tissue injury.
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