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Amyloid disorders were first discovered almost 300 years ago in patients with long-standing chronic
infections or inflammation. In the nineteenth century, it was reported that many diseases were
accompanied by specific microscopically recognizable tissue changes. One particular pattern of
tissue damage was named "amyloidosis" based on its staining characteristics upon coloration
with a dye specific for a protein called amyloid (originally believed and later discredited to be
the combination of starch and a type of carbohydrate).
It was later discovered that after staining the amyloid protein appeared as a characteristic apple-green
birefringence (Figure 1) under a polarizing microscope, allowing for easy detection of fibrils in
tissues. In the 1960s, advances in electron microscopy allowed detailed studies of amyloid deposits
and plaques from the brains of patients with Alzheimer's disease. This allowed researchers to discover
that although the amyloid appeared to be a smooth amorphous mass when visualized by light microscopy, it
was actually an aggregation of tiny, needle-like amyloid protein fibrils.
By the end of the 1970s, much more information was known about the general structure of amyloid
fibrils and deposits. In the brain tissue of Alzheimer's disease patients, in particular, deposits
(plaques) were shown to be made of portions of nerve cells surrounding a core of amyloid deposits.
Biochemical studies demonstrated that many amyloid proteins within the amyloid family could
precipitate as fibrils to form amyloid protein deposits in a variety of organs and tissues.
Figure 1
Splenic amyloid deposits stained with Congo Red
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