The exact cause of multiple myeloma is not known as of 2015, states Mayo Clinic. Normally, multiple myeloma begins as a condition called monoclonal gammopathy, or MGUS, which is benign. Approximately 1 percent of people with MGUS develop multiple myeloma.
Research shows that both multiple myeloma and MGUS patients have M proteins in the body, which are produced by abnormal plasma cells, according to Mayo Clinic. However, patients with MGUS have a much lower level of M proteins, and MGUS does not harm the body the way multiple myeloma does. Multiple myeloma begins with the presence of one abnormal cell in a person's bone marrow. These abnormal cells reproduce, and healthy cells are destroyed. This leads to fatigue and the inability to fight infections.
Healthy plasma cells produce antibodies, as explained by Mayo Clinic. However, the abnormal plasma cells that are present in patients with multiple myeloma cause the production of abnormal antibodies. The human body cannot use these abnormal antibodies. This results in a build up of M proteins, which can lead to serious medical issues such as kidney damage. Some factors that may increase a person's risk of developing multiple myeloma include aging, a history of MGUS and being male.