Amyloid

Author: Prof. Dr. med. Peter Altmeyer

Last updated on: 21.12.2021

Definition
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Extracellularly stored glycoproteins characterized by common staining, biochemical and ultrastructural properties, see also amyloidosis. Amyloid is a "waste product" that can hardly be taken up and degraded by macrophages. It differs from all other human proteins and consists for the most part of unbranched, rigid fibrils (see below) whose polypeptide chains mostly have a beta-sheet structure. All amyloid types contain a non-fibrillar component derived from the physiological serum component serum-alpha-globulin (SAP) as well as glycosaminoglycans. Different proteins, e.g. keratin, immunoglobulins, insulin and beta2-microglobulin can be deposited as amyloid.

In HE section: Amorphous, eosinophilic, homogeneous material.
In Congo red stain: metachromasia.
In polarized light: green glow.
In fluorescence microscopy: Yellow brightening after thioflavin T staining.
Ultrastructural: Linear unbranched fibrils with a diameter of 7.5 to 10 nm.

In addition to the fibrillar component, 10% of amyloid consists of a non-fibrillar substance, the so-called P-component.

Note(s)
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So far > 20 amyloidogenic proteins are known (see below amyloidosis systemic)

Literature
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Abels C (2001) Truss-induced macular amyloidosis. dermatologist 52: 970-973
Breathnach SM (1988) Amyloid and amyloidosis. J Am Acad Dermatol 18: 1-16
Fujimoto N et al (2002) Coexistence of beta2 microglobulin and lambda light chain in amyloid fibrils of dialysis-unrelated plasma cell dyscrasia-associated systemic amyloidosis. Br J Dermatol 147: 549-553
Merlini G et al (2003) Molecular mechanisms of amyloidosis. N Engl J Med 349: 583-596
Moon AO et al (2003) Nodular amyloidosis: review and long-term f-up of 16 cases. Arch Dermatol 139: 1157-1159
Ruzicka T, Donhauser G, Left RP, Landthaler M Bieber T (1990) Cutaneous amyloidosis. dermatologist 41: 245-255
Vecchietti G et al (2003) An unusual form of primary systemic amyloidosis: amyloid elastosis: report of a case treated by haematopoietic cell transplantation. Br J Dermatol 148: 154-159
Woollons A et al (2001) Nodular localized primary cutaneous amyloidosis: a long-term follow-up study. Br J Dermatol 145: 105-109

Tables
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Amyloid protein	Pathogenetic significance
AA	Amyloid A fibril protein(AA=amyloid associated). The precursor protein is the serum amyloid A protein (SAA), an acute phase protein. The AA protein is found in the amyloid after long-term chronic inflammation (secondary amyloidosis) and in hereditary diseases such as familial Mediterranean fever and Muckle-Wells syndrome (AA amyloidosis, urticaria and hearing loss). AA-amyloidosis also occurs without previous illness as primary AA-amyloidosis.
AL	Amyloid of the immunoglobulin light chain type(AL=amyloid light). Precursor proteins are monoclonal immunoglobulin light chains. According to the iso and idiotypes, AL proteins are chemically diverse. Two skin types are distinguished:_Aκ and_Aλ. This amyloid occurs in a number of very different forms of amyloidosis, such as benign monoclonal gammopathy and malignant monoclonal B-cell proliferation (multiple myeloma, Bence-Jones plasmacytoma, Waldenström's disease, heavy chain disease, etc.).
ATTR	Fibril proteins in familial amyloidoses derived from variants of prealbumin/transthyretin. The proteins are found in a number of different polyneuropathies, the best known of which is the Portuguese type in which the amino acid valine in position 30 of the prealbumin is replaced by methionine.
ASc1	Senile cardiovascular (senile cardiac) amyloid of the prealbumin/transthyretin type. As far as is known, this protein has no amino acid exchange. It is not familial, but strongly age-dependent. Therefore this form is also called "Greisenamyloid". It affects not only the cardiovascular system, but also the lungs, the larger vessels and joint structures.
ASc2	Senile atrial amlyoid. It's derived from the atrial natriuretic peptide. This form of amyloidosis is one of the most common; ASc2 is also strongly age-dependent. This form of amyloidosis is found in most people after the age of 90.
AB	Amyloid on hemodialysis. Serum precursor is beta-2 microglobulin. The AB amyloid is deposited in the area of large joints in the connective tissue apparatus, the synovial membrane and in the bone. Amyloidomas are formed in the bone marrow, which can cause bone arrosion, resulting in pathological fractures.
Aβ	This protein (β protein A4 protein) is found in Alzheimer's disease and congophilic angiopathy. It leads to peripheral, cerebral mass bleeding. Its deposition is also associated with typical loss of brain function in the sense of senile dementia.
AC	A cytokine C variant is deposited. AC occurs in hereditary Icelandic apoplexy.
AEt	Amyloid (endocrine) in medullary thyroid carcinoma, is derived from thyreocalcitonin.
AEi	Amyloid (endocrine) in the islets of the pancreas ("pancreatic hyalinosis") in type II diabetes Amyloid fibril protein (IPP) is not insulin but a new hormone of the calcitonin family.
ASAF/APrP	Scrapie-associated fibril protein. Characteristic cerebral protein with amyloid structure in the form of "naked" drusen in Jacob-Kreutzfeld and Gerstmann-Sträußler disease. The scrapie disease of various animals (hamster, sheep, cattle) also belongs to this type. This is an agent that is "infectious" and described as a "slow virus". It is called a "prion" and contains a defined protein (PrP).
AK	Keratin peptides are assumed to be the starting material for the formation of amyloid in lichen amyloidosus and macular amyloidosis. This assumption is not yet confirmed. Some experimental findings support this thesis (monoclonal antibodies, amino acid sequence analysis of individual peptides and electron-optical findings).