In
medicine,
amyloidosis refers to a variety of conditions in which
amyloid proteins are abnormally deposited in
organs and/or
tissues. A protein is described as being amyloid if, due to an alteration in its
secondary structure, it takes on a particular aggregated
insoluble form similar to the
beta-pleated sheet.
Symptoms vary widely depending upon the site of amyloid deposition. Amyloidosis may be inherited or acquired.
Classification
Amyloidosis may be divided into the following types:
[James, William; Berger, Timothy; Elston, Dirk (2005). Andrews' Diseases of the Skin: Clinical Dermatology. (10th ed.). Saunders. ISBN 0721629210.]Diagnosis
Amyloid can be diagnosed on microscopic examination of affected tissue. Extracellular amyloid deposits can be identified
histologically by
Congo red staining
and viewing under
polarized light where amyloid deposits produce a distinctive
apple green birefringence. Other more specific tests are available to more precisely identify the amyloid protein.
Biopsies are taken from affected organs (for example, the
kidney), or often in the case of systemic amyloid, from the
rectum,
gingiva, or
omentum (anterior abdominal
adipose tissue).
In addition, all amyloid deposits contain
serum amyloid P component (SAP),
a circulating protein of the
pentraxin family.
Radionuclide SAP scans have been developed which can anatomically localize amyloid deposits in patients.
Bleeding under the skin, called
amyloid purpura, is seen in a minority of patients with amyloidosis.
This type of lesion may be pronounced in the periorbital area.
Histology: amorphous; eosinophilic; extracellular material; extracted amyloid has pentagonal structures, the P component.
Classification of amyloid
The modern classification of amyloid disease tends to use an abbreviation of the protein that makes up the majority of deposits, prefixed with the letter A. For example amyloidosis caused by transthyretin is termed "ATTR". Deposition patterns vary between patients but are almost always composed of just one amyloidogenic protein. Deposition can be systemic (affecting many different organ systems) or organ-specific. Many amyloidoses are
inherited, due to
mutations in the precursor protein. Other forms are due to different diseases causing overabundant or abnormal protein production - such as with over production of
immunoglobulin light chains in
multiple myeloma (termed AL amyloid), or with continuous overproduction of
acute phase proteins in
chronic inflammation (which can lead to AA amyloid).
Out of the approximately 60 amyloid proteins that have been identified so far,
at least 36 have been associated in some way with a human disease.
Standard classification
Following is a brief description of the more common types of amyloid:
OMIM includes the following:
Alternative classifications
An older, clinical, method of classification refers to the amyloidoses as
systemic or
localised- Systemic amyloidoses are those which affect more than one body organ or system. Examples are: AL, AA and Aβ2m.
[ Table 5-12 in: 8th edition. ]
Another classification is
primary or
secondary.
- Primary amyloidoses arise from a disease with disordered immune cell function such as multiple myeloma and other immunocyte dyscrasias.
- Secondary (reactive) amyloidoses are those occurring as a complication of some other chronic inflammatory or tissue destructive disease. Examples are reactive systemic amyloidosis.
Famous people who have been affected by amyloidosis
- Lois E, Hautamaki, Educator/Principal at Heritage Christian Academy, Maple Grove, Minnesota
- Chip Miller, cofounder of the Automotive Shows at Carlisle,Pennsylvania.
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