Amyloidosis in Hematologic Disorders

Amyloidosis is a group of conditions in which normally soluble proteins misfold and deposit as insoluble amyloid fibrils in tissues, disrupting organ function. In hematology the central form is immunoglobulin light chain (AL) amyloidosis, in which a clonal plasma cell or B-cell population produces light chains that misfold and aggregate. This entry frames amyloidosis as it arises from clonal plasma cell and lymphoproliferative disease.

Definition

Amyloidosis is the deposition of misfolded proteins as insoluble amyloid fibrils in tissues; in its principal hematologic form, immunoglobulin light chain (AL) amyloidosis, a clonal plasma cell or B-cell population produces light chains that misfold and deposit, causing progressive organ dysfunction.

Scope

This entry covers the general concept of amyloid fibril formation, the hematologic form (AL amyloidosis) driven by a clonal plasma cell or B-cell population, the relationship between the clonal protein and tissue deposition, and the importance of distinguishing AL from non-hematologic amyloid types. It is a reference description and not clinical management guidance.

Core questions

• How do soluble proteins misfold into amyloid fibrils?
• What links a plasma cell clone to AL amyloidosis?
• How does AL amyloidosis differ from non-hematologic amyloid types?
• Why does identifying the amyloid protein type matter?

Key concepts

• Amyloid fibril
• Protein misfolding and aggregation
• Immunoglobulin light chain (AL) amyloidosis
• Clonal plasma cell / B-cell population
• Amyloid typing
• Organ deposition and dysfunction
• Distinction from transthyretin and other amyloid types

Mechanisms

Amyloidosis results when a precursor protein adopts a misfolded conformation that assembles into highly ordered, insoluble fibrils with a characteristic structure; these fibrils accumulate in the extracellular space and impair organ function. In AL amyloidosis the precursor is a monoclonal immunoglobulin light chain produced by a clonal plasma cell or B-cell population, linking the disorder directly to the lymphoproliferative and plasma cell diseases; the intrinsic propensity of the particular light chain to misfold helps determine whether and where amyloid deposits. Because many different proteins can form amyloid, identifying the specific fibril protein (typing) is essential to separate AL amyloidosis from non-hematologic forms such as transthyretin amyloidosis.

Clinical relevance

Amyloidosis is a reference example of how protein misfolding causes disease and of how a clonal hematologic process can damage organs through a secreted protein rather than tumour bulk. Recognising the hematologic (AL) form and the need to type the amyloid clarifies its place within plasma cell and lymphoproliferative disorders. This entry describes the disease conceptually and is not a basis for individual diagnosis or treatment.

Epidemiology

AL amyloidosis is uncommon and occurs mainly in older adults. It is closely related to clonal plasma cell disease and can coexist with or arise in the setting of monoclonal gammopathy, multiple myeloma, or other B-cell disorders; non-hematologic amyloid types, such as transthyretin amyloidosis, have separate epidemiology and are considered chiefly to ensure correct typing.

History

The term amyloid dates to the nineteenth century, when deposits were mistakenly thought to be starch-like. Twentieth-century work established their fibrillar protein nature and the diversity of precursor proteins, and the recognition that immunoglobulin light chains underlie AL amyloidosis tied the hematologic form to clonal plasma cell disease. Advances in amyloid typing later made reliable distinction between AL and other amyloid types central to understanding the disorder.

Debates

Why some light chains form amyloid

Not every monoclonal light chain produces amyloidosis, and the structural and biophysical properties that make a particular light chain prone to misfold and deposit remain an area of active investigation.

Key figures

• Giampaolo Merlini
• Vittorio Bellotti
• Giovanni Palladini

Seminal works

• merlini-2003
• merlini-2017
• palladini-2022

Frequently asked questions

What is AL amyloidosis?

AL (immunoglobulin light chain) amyloidosis is the hematologic form of amyloidosis, in which a clonal plasma cell or B-cell population produces light chains that misfold and deposit as amyloid fibrils in organs. It is linked to plasma cell and lymphoproliferative disease.

Why is it important to type the amyloid?

Because many different proteins can form amyloid, identifying the specific fibril protein distinguishes the hematologic AL form from non-hematologic types such as transthyretin amyloidosis. Correct typing is essential because the underlying causes differ fundamentally.