Mutations in the AICDA gene leading to AID inactivation are associated with hyper-IgM syndrome type 2 (HIGM2), which is an immunodeficiency type characterized by increased IgM class antibody content in blood, accompanied by the almost complete absence of IgG, IgE and IgA class antibodies [22]. Here, IGHE is linked to hyper-IgM syndrome type 2.