Amyloidosis is a group of diseases characterized by deposition of abnormal fibrillar proteins in tissues and organs. The document discusses the physical and chemical nature of amyloid, including that it is composed mainly of fibril proteins arranged in beta-pleated sheets, as well as non-fibrillar components. It describes the different types of fibril proteins that can compose amyloid deposits, including immunoglobulin light chains (AL), serum amyloid A (AA), and others. The document provides details on the staining characteristics, diagnosis, morphologic features in organs, and prognosis of amyloidosis.

1. AMYLOIDOSIS
• Amyloidosis is the term used for a group of diseases characterised by
extracellular deposition of fibrillar proteinaceous substance called
amyloid having common morphological appearance, staining properties
and physical structure but with variable protein (or biochemical)
composition.
PHYSICAL AND CHEMICAL NATURE OF AMYLOID
• It emerges that on the basis of morphology and physical characteristics, all
forms of amyloid are similar in appearance, but they are chemically
heterogeneous.

2. • Based on these analysis, amyloid is composed of 2 main types of complex
proteins:
 Fibril proteins comprise about 95% of amyloid.
 Non-fibrillar components which include P-component predominantly;
there are several different proteins which together constitute the
remaining 5% of amyloid.
Fibril Proteins
• By electron microscopy, it became apparent that major component of all
forms of amyloid (about 95%) consists of meshwork of fibril proteins.
• The fibrils are delicate, randomly dispersed, non-branching, each
measuring 7.5-10 nm in diameter and having indefinite length.
• Each fibril is further composed of double helix of two pleated sheets in the
form of twin filaments separated by a clear space.

3. • By X-ray crystallography and infra-red spectroscopy, the fibrils are shown to
have cross-β-pleated sheet configuration which produces 1000 A°.
• Chemical analysis of fibril proteins of amyloid reveals heterogeneous nature of
amyloid. These proteins can be categorised as under:
 AL (amyloid light chain) protein
 AA (amyloid associated) protein
 Other proteins

5. • AL PROTEIN. AL amyloid fibril protein is derived from immunoglobulin
light chain, which in most cases includes amino-terminal segment of the
immunoglobulin light chain and part of C region.
• AL type of fibril protein is produced by immunoglobulin secreting cells and
is therefore seen in association with plasma cell dyscrasias and is included
in primary systemic amyloidosis.
• AA PROTEIN. AA fibril protein is composed of protein which is derived
from larger precursor protein in the serum called SAA (serum amyloid
associated protein)
• In the plasma, SAA circulates in association with HDL3 (high-density
lipoprotein).
• SAA fibril protein is found in secondary amyloidosis which includes the
largest group of diseases associated with amyloidosis.

7. OTHER PROTEINS
1 Transthyretin (TTR) It is a serum protein synthesised in the liver and
transports thyroxine and retinol normally (trans-thy-
retin).
2 Aβ2-microglobulin
(Aβ2M)
Seen in cases of long-term haemodialysis (for 8-10
years)and a normal component of major
histocompatibility complex (MHC)
3 β-amyloid protein
(Aβ).
Seen in cerebral plaques as well as cerebral blood vessels
in Alzheimer’s disease
4 Immunoglobulin
heavy chain amyloid
(AH)
Derived from truncated heavy chain of immunoglobulin
and is an uncommon form of systemic amyloidosis
5 Amyloid from
hormone precursor
proteins
Examples such as amyloid derived from pro-calcitonin
(ACal), proinsulin (AIns), prolactin (APro), atrial natriuretic
factor (AANF)
6 Amyloid of prion
protein (APrP)
Derived from precursor prion protein which is a plasma
membrane glycoprotein, lacking in RNA or DNA.

8. II. Non-fibrillar Components
1. Amyloid P (AP)-component. It is synthesised in the liver and is present in all
types of amyloid. It is derived from circulating serum amyloid P-component, a
glycoprotein resembling the normal serum α1-glycoprotein and is PAS positive.
2. Apolipoprotein-E (apoE). It is a regulator of lipoprotein metabolism and is
found in all types of amyloid. One allele, apoE4, increases the risk of Alzheimer
precursor protein(APP) deposition in Alzheimer’s disease but not in all other
types of amyloid deposits.
3. Sulfated glycosaminoglycans(GAGs). These are constituents of matrix proteins;
particularly associated is heparan sulfate in all types of tissue amyloid.
4. α-1 anti-chymotrypsin. It is seen in cases of AA deposits only but not seen in
primary amyloidosis.
5. Protein X. This protein has been shown to be present in cases of prionoses.
6. Other components. Besides above, components of complement, proteases,
and membrane constituents may be seen.

10. Deposition of AL Amyloid
1. The stimulus for production of AL amyloid is some disorder of
immunoglobulin synthesis e.g. multiple myeloma, B cell lymphoma, other
plasma cell dyscrasias.
2. Excessive immunoglobulin production is in the form of monoclonal
gammopathy i.e. there is production of either intact immunoglobulin, or λ
light chain, or κ light chain, or rarely heavy chains. This takes place by
monoclonal proliferation of plasma cells, B lymphocytes, or their
precursors.
3. Partial degradation in the form of limited proteolysis of larger protein
molecules occurs in macrophages that are anatomically closely associated
with AL amyloid.
4. Non-fibrillar components like AP and GAGs play some role in folding and
aggregation of fibril proteins.

11. Deposition of AA Amyloid
1. AA amyloid is directly related to SAA levels, a highdensity lipoprotein. SAA is
synthesised by the liver in response to cytokines, notably interleukin 1 and 6,
released from activated macrophages.
2. The levels of SAA are elevated in long-standing tissue destruction e.g. in chronic
inflammation, cancers. However, SAA levels in isolation do not always lead to AA
amyloid.
3. As in AL amyloid, partial degradation in the form of limited proteolysis takes place
in reticuloendothelial cells.
4. In AA amyloid, a significant role is played by another glycoprotein, amyloid
enhancing factor (AEF). The exact composition of AEF is not known. AEF is
elaborated in chronic inflammation, cancer and familial Mediterranean fever. On
the basis of experimental induction of AA amyloid, AEF has been shown to
accelerate AA amyloid deposition. Possibly, AEF acts as a nidus for deposition of
fibrils in AA amyloid.
5. As in AL amyloid, there is a role of AP component and glycosaminoglycans in the
fibril protein aggregation and to protect it from disaggregation again.

12. CLASSIFICATION OF AMYLOIDOSIS

14. STAINING CHARACTERISTICS OF AMYLOID

15. DIAGNOSIS OF AMYLOIDOSIS
1. BIOPSY EXAMINATION. Histologic examination of biopsy material is the commonest
and confirmatory method for diagnosis in a suspected case of amyloidosis.
 kidney biopsy
 rectal biopsy
 gingiva and skin biopsy
2. IN VIVO CONGO RED TEST. A known quantity of Congo red dye may be injected
intravenously in living patient. If amyloidosis is present, the dye gets bound to
amyloid deposits and its levels in blood rapidly decline.
3. OTHER TESTS. A few other tests are
 protein electrophoresis
 immunoelectrophoresis of urine and serum
 bone marrow aspiration.

16. MORPHOLOGIC FEATURES OF AMYLOIDOSIS OF ORGANS
• Grossly, the affected organ is usually enlarged, pale and rubbery. Cut
surface shows firm, waxy and translucent parenchyma which takes
positive staining with the iodine test.
• Microscopically, the deposits of amyloid are found in the extracellular
locations, initially in the walls of small blood vessels producing
microscopic changes and effects, while later the deposits are in large
amounts causing macroscopic changes and effects of pressure atrophy.

17. PROGNOSIS OF AMYLOIDOSIS
• The prognosis of patients with generalised amyloidosis is generally poor.
• Primary amyloidosis, if left untreated, is rapidly progressive and fatal.
Therapy in these cases is directed at reducing the clonal marrow plasma
cells as is done for treatment of multiple myeloma.
• For secondary reactive amyloidosis, control of inflammation is the
mainstay of treatment. Secondary amyloidosis has somewhat better
outcome due to controllable underlying condition.
• Renal failure and cardiac arrhythmias are the most common causes of
death in most cases of systemic amyloidosis.