Monoclonal gammopathy of undetermined significance (MGUS) is a condition in which an abnormal protein — known as monoclonal protein or M protein — is in your blood.

This abnormal protein is formed within your bone marrow, the soft, blood-producing tissue that fills in the center of most of your bones. The disorder occurs most commonly in older men.

MGUS usually causes no problems. But sometimes it can progress to more-serious diseases, including some forms of blood cancer.

If you have high amounts of this protein in your blood, it's important to have regular checkups so that you can get earlier treatment if it does progress. If there's no disease progression, MGUS doesn't require treatment.

Monoclonal gammopathy of undetermined significance (MGUS) care at Mayo Clinic


People with monoclonal gammopathy generally don't experience signs or symptoms. Some people may experience a rash or nerve problems, such as numbness or tingling. MGUS is usually detected by chance when you have a blood test for another condition.


The precise cause of MGUS isn't known. Genetic changes and environmental triggers appear to play a role.

Risk factors

Factors that increase your risk of developing MGUS include:

  • Age. The average age at diagnosis is 70 years.
  • Race. Africans and African Americans are more likely to experience MGUS than are white people.
  • Sex. MGUS is more common in men.
  • Family history. You may have a higher risk of MGUS if other people in your family have the condition.


Each year about 1% of people with MGUS go on to develop certain types of blood cancers or other serious diseases such as:

  • Multiple myeloma
  • Light chain amyloidosis
  • Waldenstrom macroglobulinemia
  • Lymphoma

Other complications associated with MGUS include bone fractures, blood clots and kidney problems.