IDs can be grouped as follows: combined B and T cell immunodeficiencies, deficiencies predominantly affecting antibody production, defects in lymphocyte apoptosis, other well-defined immunodeficiency syndromes, defects of phagocyte function, interferon-γ (IFNγ) associated immunodeficiencies, DNA breakage associated syndromes, defects of the complement cascade proteins, and defects of complement regulatory proteins. Here, IFNG is linked to immunodeficiency disease.