Selective IgM Immunodeficiency

**Semantic type:** Disease or Syndrome

**Definition:** A rare dysgammaglobulinemia characterized by low or undetectable serum levels of immunoglobulin class M (IgM). It is an uncommon primary antibody deficiency. It is most likely an inherited immunodeficiency. It may be caused by decreased or inefficient production of IgM from progenitor B cells without any corresponding decreases in the other isotypes. There is a widely variable clinical course. Some affected individuals may be asymptomatic while others show increased susceptibility to infection, malignancy and autoimmune disorders.