Amyloidosis

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What is Amyloidosis?

Amyloidosis refers to a group of disease where there is abnormal deposition of an insoluble protein in various body tissues and organs. Excessive deposition of amyloid may lead to serious changes in organ structure and function.

There are over 20 types of different proteins involved, each causing a type of amyloid disease. The type of amyloid disease is defined by the major fibrillar protein contained.

Amyloidosis can be systemic (where there is protein deposition in various parts of the body) or organ-specific (limited to one organ).

Who gets Amyloidosis?

Amyloidosis is a relatively rare condition, with the number of new cases per year being about 8 in a million. Patients are usually affected after middle age, and the disease appears to affect all races equally.

In developed countries, light chain amyloidosis (AL) is the most common type of systemic amyloidosis, while in developing countries another type called AA amyloidosis is more frequent.

Predisposing Factors

The modern way of classifying amyloidosis is based on the biochemical structure, i.e. the main fibril protein involved.

The amyloidoses are referred to with 2 capital letters: a capital A (for amyloid) followed by an abbreviation for the fibril protein contained. For example, in a type of amyloidosis called light chain amyloidosis (abbreviated AL), the capital A stands for amyloid, and the capital L stands for the fibril protein which, in this type of amyloidosis, is immunoglobulin light chain or light chain fragment (abbreviated L), hence the abbreviation AL.

The most common types of amyloidosis seen are the AL and AA types.

As mentioned above, AL amyloidosis (formerly known as primary amyloidosis) is due to deposition of protein derived from immunoglobulin light chain fragments. It can occur alone or in association with other diseases e.g. multiple myeloma, Waldenstrom's macroglobulinaemia, or non-Hodgkin's lymphoma.

In AA amyloidosis (formerly known as secondary amyloidosis), the main fibril protein is serum amyloid A protein (abbreviated A), giving rise to the abbreviation AA for the disease. Amyloidosis may occur as a result of chronic diseases with ongoing inflammation, such as rheumatoid arthritis (RA), osteomyelitis, tuberculosis, Hodgkin's lymphoma, kidney cancer, leprosy, Chron's disease, AIDS, lupus etc.

There are other types of amyloidosis, e.g. dialysis-related amyloidosis (which occurs in patients on long-term dialysis), familial amyloidosis (caused by inherited gene abnormalities), systemic senile amyloidosis (which is an age-related amyloidosis).

Progression

In the two most common forms of systemic amyloidosis, AL and AA amyloidoses, the major sites involved are the kidneys, heart, and liver.

Amyloid deposition can be limited to a single organ, such as the skin, eye, heart, pancreas, reproductive tract and urinary tract.

Hereditary amyloidosis is characterised by impairment of nerves, as well as amyloid deposition in the heart, vessels, and kidneys. Carpal tunnel syndrome may occur.

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