Variants in TNFRSF9 cause immunodeficiency 109 with lymphoproliferation (IMD109, OMIM #620282), a rare autosomal recessive disorder characterized by immunodeficiency, recurrent infection, hypogammaglobulinemia, EBV viremia, and EBV-induced lymphoproliferative disorders or lymphoma (9). The gene discussed is TNFRSF9; the disease is immune system disorder.