Pathogenic variants in CTLA4, LRBA, TNFRSF13B (TACI), DOCK8, RAG1, PRF1, PIK3CD, IKZF1, and PRKDC have been identified in patients with AICs and PIDs, often associated with other clinical features such as lymphoproliferation, splenomegaly, and immunologic abnormalities such as hypogammaglobulinemia [10–12]. The gene discussed is TNFRSF13B; the disease is Splenomegaly.