Amyloidosis

Amyloid describes various types of protein aggregations that share specific traits when examined microscopically. The name amyloid comes from the early mistaken identification of the substance as starch (amylum in Latin), based on crude iodine-staining techniques. For a period, the scientific community debated whether or not amyloid deposits were fatty deposits or carbohydrate deposits until it was finally resolved that it was neither, but rather a deposition of proteinaceous mass. more...

To be specific, amyloid deposits are extracellular, thioflavin-positive, and exhibit apple-green birefringence when stained with congo red. Other indicators exist, such as serum amyloid p-component binding. Since these are indirect indicators, biophysicists have redefined amyloid using a canonical set of biophysical characteristics (see below), and this seems to cause a low level of conflict between histologists and biophysicists.

The phenotypes of genetically-transmitted amyloid diseases are often inherited in an autosomal dominant fashion. Sometimes, the difference between aggressive amyloid diseases and senescent amyloid diseases is due to a mutation that makes the protein more prone to aggregation. Most commonly seen are point mutations, which affect the cohesiveness of the protein and promote misfolding; other mutations cause aggregation-prone pieces of the protein to be cleaved off from the rest of the protein.

Diseases featuring amyloid

It should be noted that, in almost all of the organ-specific pathologies, there is significant debate as to whether the amyloid plaques are the causal agent of the disease or instead a symptom downstream of a common ideopathic agent. The associated proteins are indicated in parentheses. Note that amyloidosis by itself ususally refers to AA amyloidosis, but any disease which presents amyloid deposition is technically an amyloidosis. CJD, alzheimer's and diabetes are almost never referred to as amyloidoses.

• Systemic amyloidosis
  • Primary amyloidosis
    • Mutations in lysozyme, transthyretin, apolipoprotein B, fibrinogen
  • Secondary amyloidosis
    • AA amyloidosis (amyloid A protein, an acute-phase protein due to chronic inflammation)
    • AL amyloidosis (immunoglobulin light chains)
    • Gelsolin amyloidosis (plasma gelsolin fragments).
  • Familial or Hereditary amyloidosis
    • Most commonly caused by mutations in the transthyretin protein, but in rare occurrences can also be caused by apolipoprotein A1, gelsolin, fibrinogen, and lysozyme mutations.
    • Primarily caused by genetics, believed to be autosomal dominant, high probability of passage to offspring
    • Appalachian type amyloidosis
• Organ-specific amyloidosis
  • Diabetes mellitus type 2 (amylin, also known as IAPP)
  • Neurology
    • Alzheimer's disease (Aβ 39-42)
    • Parkinson's disease (alpha-synuclein) -- biophysical definition
    • Huntington's disease (huntingtin) -- biophysical definition
    • Spongiform encephalopathies
      • Creutzfeldt-Jakob disease (PrP in cerebrum)
      • Kuru (diffuse PrP deposits in brain)
      • Fatal Familial Insomnia (PrP in thalamus)
      • Bovine spongiform encephalopathy (PrP in cerebrum)
    • Congophilic angiopathy (Amyloid beta)
    • congestive heart failure; some instances (PrP in heart)
  • Inclusion body myositis
• Iatrogenic conditions
  • insulin amyloidosis (injection-administered insulin)

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