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Perth Haematology :: Dr Steven Ward

Amyloid

 

Amyloidosis results from a sequence of changes in protein folding that leads to the deposition of insoluble amyloid fibrils, mainly in the extracellular spaces of organs and tissues. Depending upon the biochemical nature of the amyloid precursor protein, amyloid fibrils can be deposited locally or may involve virtually every organ system of the body. Amyloid fibril deposition may have no apparent clinical consequences or may be associated with severe disease.  All amyloid fibrils share an identical secondary structure, the β-pleated sheet. All amyloid deposits contain the pentraxin serum amyloid P (SAP) and glycosaminoglycans. Abnormal protein folding and assembly can also result in protein deposition (e.g., in brain or kidney) that lacks the classic fibrillar morphology of amyloid and the presence of SAP.

 

The amyloidoses are classified according to the identity of the fibril-forming protein (See below). Systemic amyloidoses are neoplastic, inflammatory, genetic, or iatrogenic in origin, while localized amyloidoses or organ-limited amyloidoses are associated with aging and diabetes and occur in isolated organs without evidence of systemic involvement.

 

Despite their biochemical and clinical differences, the various amyloidoses share common pathophysiologic features:

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a precursor substance in appropriate concentration;

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appropriate host genetic background;

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abnormalities in proteolysis of fibril precursors and nascent amyloid fibrils;

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alterations in extracellular matrix constituents such as glycosaminoglycans and Apo E.

 

 

Amyloid Fibril Proteins and Their Precursors

Amyloid Protein

Precursor

Systemic (S) or Localized (L)

Syndrome or Involved Tissues

AL

Immunoglobulin light chain

S, L

Primary

Myeloma-associated

AH

Immunoglobulin heavy chain

S, L

Primary

Myeloma-associated

ATTR

Transthyretin

S

Familial

Senile systemic

 

 

L?

Tenosynovium

2M
 

β2-microglobulin
 

S

L?

Hemodialysis

Joints

AA

(Apo)serum AA

S

Secondary, reactive

AApoAI

Apolipoprotein AI

S

L

Familial

Aortic

AApoAII

Apolipoprotein AII

S

Familial

AGel

Gelsolin

S

Familial

ALys

Lysozyme

S

Familial

AFib

Fibrinogen α-chain

S

Familial

ACys

Cystatin C

S

Familial

ABria
 

ABriPP

L, S?

Familial dementia, British

ADana

ADanPP 

L 

Familial dementia, Danish 

Aβ protein precursor (AβPP)

L

Alzheimer's disease, aging

APrP

Prion protein

L

Spongiform encephalopathies

ACal

(Pro)calcitonin

L

C-cell thyroid tumors

AIAPP

Islet amyloid polypeptide

L

Islets of Langerhans

Insulinomas

AANF

Atrial natriuretic factor

L

Cardiac atria

APro

Prolactin

L

Aging pituitary

Prolactinomas

Alns

Insulin

L

Iatrogenic

AMed

Lactadherin

L

Senile aortic, media

AKer

Kerato-epithelin

L

Cornea; familial

A(tbn)b

tbnb 

Pindborg tumors 

ALac 

Lactoferrin 

Cornea; familial 

Note: Proteins in italics are preliminary.

aADan  comes from the same gene as ABri and has identical N-terminal sequence. It will be a matter of further discussion whether ADan should be included in the nomenclature as a separate protein (see text)

bTo be named.

 

Light Chain Amyloidosis (AL)

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The most common form of systemic amyloidosis is AL (primary idiopathic amyloidosis, or that associated with multiple myeloma) resulting from fibril formation by fragments of monoclonal antibody light chains in primary amyloidosis and in some cases of multiple myeloma.

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Fewer than 20% of patients with AL have myeloma. The rest have other monoclonal gammopathies, light chain disease, or even agammaglobulinemia (producing light chains, but not intact immunoglobulin).

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About 15 to 20% of patients with myeloma have amyloidosis. A monoclonal population of bone marrow plasma cells is present and consistently produces either small lambda or kappa fragments or immunoglobulins that are processed (cleaved) in an abnormal fashion by macrophage enzymes to produce the partially degraded light chains responsible for AL amyloidosis.  There are three forms of human light chain–associated renal and systemic diseases: AL amyloidosis, cast nephropathy, and light chain deposition disease. Rarely, heavy chain amyloid deposition (AH) has been reported.

 

Amyloid A Amyloidosis (AA)

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AA amyloidosis (secondary, reactive, or acquired amyloidosis) occurs most frequently as a complication of chronic inflammatory disease. Effective treatment of the underlying inflammatory condition has reduced incidence in developed countries.  During inflammation, the cytokines interleukin (IL) 1, IL-6, and tumour necrosis factor (TNF) stimulate hepatic synthesis of serum amyloid A, the AA fibril precursor. Thus, effective treatment of the underlying inflammatory disorder blocks the stimulus for precursor synthesis.

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Familial deposition of the AA protein occurs in patients with the hereditary periodic fever syndromes familial Mediterranean fever (FMF), TNF receptor–associated periodic syndrome (TRAPS), Muckle-Wells syndrome (MWS), and familial cold uticaria (FCU). Colchicine treatment effectively blocks attacks of FMF and reduces the incidence of AA amyloidosis in association with FMF. FMF is an autosomal recessive disorder. FMF is caused by mutations in the gene designated MEFV that encodes a 781-amino-acid protein named pyrin that appears to be a transcription factor.

 

 

Clinical Features of Systemic Amyloidosis

Disease

Symptoms

AL (primary)

Monoclonal immunoglobulin in urine or serum plus any of the following:

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 Unexplained nephrotic syndrome

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 Hepatomegaly

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 Carpal tunnel syndrome

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 Macroglossia (large tongue)

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 Malabsorption or unexplained diarrhoea or constipation

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 Peripheral neuropathy

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 Cardiomyopathy

AA (secondary)

Chronic infection (osteomyelitis, tuberculosis) or chronic inflammation (rheumatoid arthritis, granulomatous ileitis) plus development of any of the following:

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 Proteinuria

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 Hepatomegaly

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 Unexplained gastrointestinal disease

Hereditary amyloidosis

 

Family history of neuropathy plus any of the following:

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 Early sensorimotor disassociation

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 Vitreous opacities

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 Renal disease

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 Autonomic nervous system symptoms

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 Cardiovascular disease

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 Gastrointestinal disease

No family history of neuropathy but

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 Idiopathic cardiomyopathy

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 Idiopathic renal disease

 

Kidney

Renal involvement may consist of mild proteinuria or frank nephrosis. The renal lesion is usually not reversible and in time leads to progressive renal failure and death. The prognosis does not appear to be related to the degree of the proteinuria. Treatment by peritoneal dialysis or hemodialysis or kidney transplantation improves the prognosis considerably. Hypertension is rare, except in long-standing amyloidosis.

Heart

Cardiac amyloidosis can present as intractable heart failure.

With respect to systemic amyloidoses, cardiac amyloidosis is common in primary (AL) and heredofamilial amyloidosis and very rare in the secondary (AA) form. In systemic amyloidosis, cardiac manifestations consist primarily of congestive failure and cardiomegaly (with or without murmurs) and a variety of arrhythmias.

Liver

While hepatic involvement is common except in heredofamilial amyloidosis of the TTR type, liver function abnormalities are minimal and occur late in the disease. Portal hypertension occurs but is uncommon. Intrahepatic cholestasis has been noted in about 5% of patients with AL (primary) amyloidosis. Hepatomegaly is common, and AL hepatic amyloid is usually accompanied by the nephrotic syndrome and congestive heart failure with poor prognosis. Amyloidosis of the spleen characteristically is not associated with leukopenia and anemia.

Skin

Involvement of the skin is one of the most characteristic manifestations of primary (AL) amyloidosis. In AL amyloidosis, the usually non-itchy lesions may consist of slightly raised, waxy papules or plaques that are usually clustered in the folds of the axillae, anal, or inguinal regions; the face and neck; or mucosal areas such as ear or tongue. Periorbital ecchymoses ("black eye" or "raccoon syndrome") have been reported.

Gastrointestinal Tract

Gastrointestinal symptoms are common in all systemic types of amyloidosis either from direct involvement of the gastrointestinal tract at any level or from infiltration of the autonomic nervous system with amyloid. Symptoms include obstruction, ulceration, malabsorption, haemorrhage, protein loss, and diarrhoea. Infiltration of the tongue is characteristic of primary amyloidosis (AL) or amyloidosis accompanying multiple myeloma and occasionally leads to macroglossia (large tongue). Gastrointestinal bleeding may occur from any of a number of sites, notably the esophagus, stomach, or large intestine, and may be severe.  A malabsorption syndrome is common.

Nervous System

Neurologic manifestations, especially prominent in the heredofamilial amyloidoses, may include peripheral neuropathy, postural hypotension, inability to sweat, Adies's pupil, hoarseness, and sphincter incompetence. The cranial nerves are generally spared, except in the Finnish hereditary amyloidosis (AGel). Carpal tunnel syndrome may be caused by several amyloidoses, especially primary (AL) and chronic hemodialysis (Aβ2M) amyloid. Peripheral neuropathy is frequent in the former type.

Endocrine

Amyloid may infiltrate the thyroid or other endocrine glands but rarely causes endocrine dysfunction.

Joints and Muscles

Amyloid can directly, although rarely, involve articular structures by its presence in the synovial membrane and synovial fluid or in the articular cartilage. In these cases it is almost always of the AL type and associated with multiple myeloma. Amyloid arthritis can mimic a number of the rheumatic diseases because it can present as a symmetric arthritis of small joints with nodules, morning stiffness, and fatigue. Amyloid infiltration of muscle may lead to a pseudomyopathy.

Respiratory System

The nasal sinuses, larynx, and trachea may be involved by accumulation of AL amyloid, which blocks the ducts, in the case of the sinuses, or the air passages. Amyloidosis of the lung involves the bronchi and alveolar septa diffusely. The lower respiratory tract is affected most frequently in primary (AL) amyloidosis and in the disease associated with dysproteinemia. Pulmonary symptoms attributable to amyloid are present in about 30% of cases. Amyloid may be localized in the bronchi or pulmonary parenchyma and may resemble a neoplasm. In these cases, local excision should be attempted and, when successful, may be followed by prolonged remissions.

Hematopoietic System

Hematologic changes may include hypofibrinogenoaemia, increased fibrinolysis, and selective deficiency of clotting factors. Deficient factor X seems to be due to non-specific calcium-dependent binding to the poly-anionic amyloid fibrils. Splenectomy in the patient with such a factor X deficiency can relieve the deficiency and the associated bleeding disorder, since factor X has been shown to bind to the large masses of splenic amyloid. Endothelial damage together with the clotting abnormalities lead to a propensity toward abnormal bleeding.

 

 

Diagnosis

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Amyloid fibrils are identified in biopsy of tissue sections. The systemic amyloidoses offer a choice of biopsy sites; abdominal fat aspirates or renal or rectal biopsies are often performed. Microscopically, amyloid deposits stain pink with the hematoxylin-eosin stain and show metachromasia with crystal violet. The widely used and useful Congo red stain imparts a unique green birefringence when stained tissue sections are viewed using the polarizing microscope. Fluorescent dyes such as thioflavin are sensitive screening stains for amyloid deposits in brain and other tissues.

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After amyloid has been identified by staining, it should be chemically classified by genomic DNA and protein studies and by immunohistochemistry.

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In order to establish the relationship of immunoglobulin-related amyloid to multiple myeloma, electrophoretic and immunoelectrophoretic studies on serum and urine should be performed when the biopsy reveals amyloid deposition. Most of these patients will have only relatively small paraprotein components, and only a few will have frank multiple myeloma. If AL and familial amyloidosis have been ruled out, AA amyloidosis should be suspected in patients with renal amyloid and a chronic inflammatory condition

 

BIOPSY

Common sites

 Subcutaneous abdominal fat aspirate

 Rectum

 Skin

 Gingiva

Occasional sites

 Small intestine

 Muscle

 Nerve

Rare sites

 Kidney

 Liver

 Bone marrow

 Synovium

 Spleen

APPROPRIATE STAIN

Congo red, viewed by polarization microscopy

Thioflavin (less specific)

PROTEIN OR DNA STUDIES

Mutant protein identification

Immunocytochemistry: immunofluorescent or immunoperoxidase stains with specific antisera

 

Symptoms, Diagnosis, and Treatment of Systemic Amyloidosis

AL (Primary)

AA (Secondary)

Familial Amyloidosis

SYMPTOMS

Unexplained nephropathy, cardiomyopathy, neuropathy

Hepatomegaly syndrome

Macroglossia

Malabsorption or unexplained diarrhea or constipation

Any of the above plus monoclonal immunoglobulin in urine

Proteinuria

Hepatomegaly and/or splenomegaly

plus

Chronic infection (osteomyelitis, tuberculosis) or chronic inflammation (rheumatoid arthritis, granulomatous ileitis)

Family history of peripheral neuropathy, nephropathy plus any of following:

Carpal tunnel syndrome

 Vitreous opacities

 Renal disease

 Autonomic nervous system symptoms

 Cardiovascular disease

 Gastrointestinal disease

 Sensorimotor disassociation

LABORATORY DIAGNOSIS

Serum, urine immunofixation electrophoresis

Bone marrow biopsy with kappa and lambda light chain immunohistochemistry

Elevated serum amyloid A (SAA)

Positive immunohistochemical staining for AA protein in tissue specimen

Identification of protein variant in serum

DNA-based test for mutant gene

TREATMENT OPTIONS

Depending upon cardiac involvement or stage of disease

 Cyclic oral melphalan and prednisolone

 High dose IV melphalan with stem cell rescue

Aggressive treatment underlying inflammatory condition (monitor SAA)

Surgical excision infection (bone resection, cholecystectemy)

Colchicine for prevention and treatment of AA amyloidosis in FMF

Organ transplantation (liver) (ATTR)

 

Prognosis

Generalized amyloidosis is usually a slowly progressive disease that leads to death if untreated. The average survival in most large series of AL amyloid is 12 months and in familial amyloidosis is 7 to 15 years. A number of individuals with amyloid have been followed 5 to 10 years and longer. The course of amyloidosis is difficult to document, because dating the time of origin of the disease is rarely possible.

 

Treatment

Rational therapy should be directed at (1) reducing precursor production, (2) inhibiting the extracellular deposition of amyloid fibrils, and (3) promoting lysis or mobilization of existing amyloid deposits.

 

There are new specific therapies for the various amyloidoses. In certain of the heredofamilial amyloidoses, genetic counselling is an important aspect of treatment, and the removal of the site of synthesis of the mutant protein by liver transplantation has proven remarkably successful.  The utilization of chronic hemodialysis and of kidney transplantation has clearly improved the prognosis of renal amyloid.

 

In the case of AL amyloid, the fact that immunoglobulin light chain is made by plasma cells has led to the use of alkylating agents. However, these agents are toxic and not very effective. The most effective form of treatment currently is stem cell transplantation and immunosuppressive drugs (melphalan). Several long-term remissions have been reported, but serious complications, even death, can occur.

Colchicine has been shown to be effective in preventing acute attacks and amyloidosis in patients with FMF.

The major causes of death are heart disease and renal failure. Sudden death, presumably due to arrhythmias, is common. Occasionally, gastrointestinal haemorrhage, respiratory failure, intractable heart failure, and superimposed infections are the terminal events.