Selective IgM Deficiency-An Underestimated Primary Immunodeficiency.

Area of Science:

• Immunology
• Primary Immunodeficiency Disorders

Background:

• Selective IgM deficiency (SIGMD) is characterized by low serum IgM with normal IgG and IgA levels.
• Despite being described decades ago, SIGMD has been historically overlooked as a primary immunodeficiency.
• It affects both pediatric and adult populations, with a higher prevalence than previously thought.

Purpose of the Study:

• To review the clinical and immunological characteristics of selective IgM deficiency.
• To discuss the potential pathogenesis and therapeutic approaches for SIGMD.
• To compare human SIGMD with relevant mouse models.

Main Methods:

• Review of existing literature on selective IgM deficiency.
• Analysis of clinical presentations, immunological findings, and treatment outcomes.
• Comparison with data from mouse models of secreted IgM deficiency.

Main Results:

• Approximately 80% of SIGMD patients present with recurrent infections (bacterial, viral, fungal, protozoal).
• Increased incidence of allergic and autoimmune diseases is noted in SIGMD patients.
• Impaired specific antibody responses to Streptococcus pneumoniae occur in over 45% of cases, while innate immunity and T cell functions remain normal.
• Mouse models lacking secreted IgM exhibit susceptibility to infections and autoimmunity, mirroring some human SIGMD features.

Conclusions:

• Selective IgM deficiency is a significant, though often underdiagnosed, primary immunodeficiency.
• Recurrent infections and specific antibody deficiencies in SIGMD patients may improve with immunoglobulin therapy.
• Further research into the pathogenesis of SIGMD is warranted.