MGUS (monoclonal gammopathy of undetermined significance)

MGUS is often diagnosed after a blood test to investigate another health condition. In most cases, people with MGUS have no symptoms and will never need treatment. The chance of MGUS developing into blood cancer is low.

On this page:

Understanding MGUS

Types of MGUS

How common is MGUS?

What causes MGUS?

What does MGUS mean?

In our bone marrow (the spongy tissue inside certain bones), we have cells called plasma cells. These cells make antibodies – Y-shaped proteins that help our bodies fight infection. They are sometimes called gamma globulins or immunoglobulins.

If you have MGUS, some of your plasma cells make abnormal antibodies called paraproteins (also known as monoclonal proteins or M-proteins). Paraproteins don’t work as well as normal antibodies and aren’t very good at fighting off infection.

Sometimes, the abnormal plasma cells only make small pieces of an antibody called light chains.

Paraproteins and light chains circulate in the bloodstream and may show up in a blood test. In MGUS, the levels are low and don’t usually cause any health problems.

MGUS itself is not blood cancer but people with MGUS do have a higher risk than normal of developing blood cancer in the future. Overall, the risk is low. Your personal level of risk depends on the levels and types of paraprotein and light chains in your blood, so your GP or hospital team will measure and monitor these.

There are five types of paraprotein: IgG, IgA, IgM, IgD and IgE. Ig stands for immunoglobulin, another name for paraprotein.

There are two types of light chain: kappa (κ) and lambda (λ). So when you get an MGUS diagnosis, you might be told the type is IgG lambda, for example. Occasionally the abnormal protein in the blood is just a kappa or lambda light chain, and no paraprotein is present. This is called light chain MGUS.

Your plasma cells will only produce one type of paraprotein. IgG is the most common type and also carries the lowest risk of progression to blood cancer.

It’s best to ask your doctor about your personal level of risk.

In the UK, around 6,000 people are diagnosed with MGUS every year.

Many people with MGUS are completely unaware of it, as they have no symptoms and it doesn’t affect how they live their life.

We don’t know what causes MGUS. We do know that you can't catch it from someone else and it’s not caused by your lifestyle.

Certain things make it more likely for someone to have MGUS:

MGUS is an abbreviation for the medical term monoclonal gammopathy of undetermined significance.

Monoclonal: This describes the abnormal antibodies in MGUS, which are clones or copies of each other.

Gammopathy: Gammopathy refers to the production of abnormal antibodies (which scientists call gamma globulins).

Undetermined significance: (or sometimes, unknown significance) This acknowledges that we don’t yet know what causes MGUS and why it progresses to blood cancer in a small number of people.

Many thanks to Dr Simon Stern and Dr Kamaraj Karunanithi for checking the accuracy of our information about MGUS.