Monoclonal paraprotein (M protein)

A **monoclonal paraprotein** is an abnormal antibody or antibody fragment produced in excess by a single clone of plasma cells. It is most commonly detected as part of disorders such as **multiple myeloma**, **MGUS** (monoclonal gammopathy of undetermined significance), Waldenström macroglobulinemia, amyloidosis, and other related hematologic diseases. These proteins are also called **M proteins**, **paraproteins**, or **myeloma proteins**. Unlike normal polyclonal antibodies that help fight infection as part of the immune system’s response to pathogens, monoclonal paraproteins are usually non-functional—they do not participate effectively in immune defense. Their presence reflects an underlying clonal proliferation disorder involving B-cells/plasma cells. Paraproteins can be whole immunoglobulin molecules or just fragments such as light chains (“Bence Jones” proteins) or heavy chains. They may be found incidentally during blood tests for unrelated reasons since many people with MGUS have no symptoms. However, high concentrations can lead to clinical problems including increased blood viscosity (“hyperviscosity syndrome”), kidney damage from deposition in renal tubules (“cast nephropathy”), suppression of normal antibody production leading to increased infection risk, neuropathy if they deposit on nerves (“amyloid neuropathy”), and other organ dysfunctions depending on where they accumulate. The detection and quantification of these abnormal proteins serve primarily as diagnostic biomarkers rather than therapeutic targets themselves—treatment focuses on eliminating the malignant plasma cell clone responsible for their production.

Other names

ParaproteinM proteinMonoclonal proteinMyeloma proteinM componentM spike