What is monoclonal gammopathy of undetermined significance (MGUS)?

In monoclonal gammopathy of undetermined significance (MGUS), blood samples contain abnormal proteins called monoclonal proteins, or M proteins. Plasma cells in the bone marrow (the soft substance at the center of bones) produce M proteins.

Normally, plasma cells produce antibodies that help your body fight infection. But people living with MGUS have plasma cells that produce unusual proteins (M proteins) instead of normal antibodies. In most cases, M proteins do not cause any problems.

MGUS itself is benign (not cancer), and most people have no symptoms. Doctors and other healthcare providers usually diagnose the condition after taking blood or urine samples as part of a routine examination. Most patients with MGUS do not need treatment. Some patients may need treatment in the future. People with MGUS need to be monitored with blood and urine testing every 6 to 12 months to determine if MGUS is progressing.

For a small percentage of individuals, the condition develops into cancerous conditions, such as multiple myeloma or lymphoma.

Who is most at risk for getting monoclonal gammopathy of undetermined significance (MGUS)?

MGUS is more common in older individuals. Individuals over the age of 50 years have a 3-5% chance of having MGUS. The highest incidence is in people age 85 or older. You may be more likely to develop MGUS if you are:

  • African-American
  • Exposed to pesticides
  • Male
  • Part of a family with a history of MGUS or multiple myeloma

How common is monoclonal gammopathy of undetermined significance (MGUS)?

Rates of MGUS climb with age. Up to 5% of people aged 70 or older are eventually diagnosed with MGUS.

What causes monoclonal gammopathy of undetermined significance (MGUS)?

MGUS results from abnormal plasma cells in bone marrow producing abnormal proteins called M proteins. Usually, plasma cells produce antibodies, which are specialized proteins that help identify and defend your body against germs. Each plasma cell produces only one type of specialized protein, or antibody.

People living with MGUS have abnormal plasma cells in addition to healthy plasma cells. These abnormal plasma cells produce M proteins instead of antibodies. M proteins circulate in the blood. They can be detected in blood and urine tests.

What are the symptoms of monoclonal gammopathy of undetermined significance (MGUS)?

MGUS usually causes no symptoms. In rare cases, people may have:

  • Tingling
  • Weakness
  • Numbness

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