Primary selective deficiency of immunoglobulin M.

Selective deficiency of IgM as a primary disorder is seldom encountered1--3, and the syndrome remains ill-defined4. It is generally accepted that for a diagnosis to be made, the serum IgM level should be consistently below 2 SD of normal, no other immunodeficiencies are present, and it is not secondary to other disease processes4. This report of an additional case may provide further insight into this rare disease.