Long-term study of a female hyper-IgM immunodeficiency

Area of Science:

• Immunology
• Genetics
• B cell biology

Background:

• Hyper-IgM immunodeficiency (HIM) is characterized by disrupted immunoglobulin class switching, leading to elevated IgM and reduced IgG/IgA.
• X-linked HIM results from defective CD40 ligand on T cells, impairing B cell signaling.
• Non-X-linked HIM presents heterogeneous causes and clinical outcomes.

Observation:

• A Japanese girl initially presented with low IgM, IgG, and IgA, evolving to a typical HIM profile with reduced IgG and increased IgM.
• Neutropenia, common in X-linked HIM, was absent.
• Despite extremely low IgG, the patient showed no severe infections without gammaglobulin therapy.

Findings:

• No mutations in CD40 ligand or CD40 were detected.
• Sequencing revealed intact immunoglobulin heavy-chain gene rearrangement in B cells, including N-region insertion.
• These findings suggest intact heavy-chain gene rearrangement in the patient's B cells.

Implications:

• The case indicates that non-X-linked HIM can occur without mutations in CD40/CD40L and with intact B cell gene rearrangement.
• The patient's resistance to infection despite low IgG suggests alternative protective mechanisms or a specific defect in class switching.
• Further research into the heterogeneous pathogenetic mechanisms of non-X-linked HIM is warranted.