Amyloidosis: An Overview
Amyloidosis is an abnormal condition whereby protein substances are deposited within the tissues of the body in the form of microscopic fibers called fibrils. It is not a single disease - at least 25 different forms have been recognized. Each is associated with the deposition of a certain protein and, in fact, the designation of a particular kind of amyloid is based on the type of protein involved. Most often, these components are found normally throughout the body or are produced locally by endocrine glands or other organs. Depending on where they are formed or deposited, some of the organs that can be affected by amyloid are kidney, heart, liver, spleen, nerves, pancreas, or brain. Notably, there are multiple diseases associated with this process; certain of these are acquired while others are inherited. Examples of amyloid-related disorders include Alzheimer's disease, the adult form of diabetes, multiple myeloma and related conditions, chronic infections, and the aging process.
Despite the differences in the composition of amyloid, as well as the diseases that result from its deposition, all forms have common features. One, when tissue that contains this material is stained with the dye Congo red and viewed with a microscope equipped with polarizing filters, the amyloid exhibits birefringence, i.e., a striking change in color from deep red to apple green and vice versa as shown in these images.
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Two, when examined under extremely high magnification with an electron microscope, amyloid appears as rigid, non-branching fibrils.
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The birefringence and rigidity result from the fact that this material has an unusual structure; namely, these proteins, like silk fibers, assemble as beta-pleated sheets. This feature renders amyloid exceptionally insoluble. Further, it is not viewed by the body as foreign or injurious and, thus, is seemingly protected from "attack" by natural defense mechanisms. Only rarely do the deposits disappear. The invasion of healthy tissue by amyloid interferes with normal body function; over time, this relentless process can lead to organ failure and death.
Over the past several decades, extensive research efforts by our laboratory and others throughout the world have provided new information on why certain proteins are deposited as amyloid and how this process occurs. These exciting leads, in addition to other recent developments, have resulted in new methods of diagnosis and strategies for treatment and prevention that ultimately will benefit patients with all types of amyloid.
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