CTLA4 and common variable immunodeficiency: 1,2 CTLA4 insufficiency is a new diagnosis, first described in 2014.1–3 Many patients had a previous diagnosis of common variable immune deficiency (CVID) and/or an autoimmune syndrome, however as availability of genetic diagnosis and awareness of the condition has improved the number of recognized cases has increased dramatically.4,5 CTLA4 insufficiency has a heterogeneous genetic landscape with no obvious hotspots, although most disease-causing mutations (>80%) are found in exons 2 and 3 (Figure 1A).1–3,5–8