With this screening assay, we selected a small series of patients who were considered CSR-like CVID cases because of an increased IgM in their serum at diagnosis (more than 2SD above the cutoff for normal values measured at least two times apart) and/or documented “IgM-only” immunoglobulin isotype production in vitro (Tables 1 and 2). This evidence concerns the gene CD40LG and common variable immunodeficiency.