CTLA4 and Lymphadenopathy: Therefore, lymphadenopathy, splenomegaly, low IgG concentrations, the absence of memory B cells, and the increase of the CD21lo B cell subset found in the patient resemble an immune dysregulation syndrome resulting from CTLA-4 haploinsufficiency with incomplete penetrance, as it has been described before for other heterozygous mutations in CTLA4 (5–7, 21, 32–34).