To further identify potential late-onset combined immunodeficiency cases (11), low class-switched memory B cell counts (CD27+ IgD− ≤2% CD19+ cells) were used as a marker of severe B cell immunopathology as previously described for CVID (10) and assayed for overlapping defects in the CD4+ T cell compartment. This evidence concerns the gene CD19 and common variable immunodeficiency.