Among the manifestations of immune dysregulation, inflammatory arthritis has emerged as an important yet underrecognized complication that may occur across multiple IEI categories, including humoral immunodeficiencies (such as X-linked agammaglobulinemia, hyper-IgM syndrome, common variable immunodeficiency, and others), complement deficiencies, disorders of immune dysregulation (STAT3 gain of function mutation, CTLA4 and LRBA haploinsufficiency), and combined immunodeficiencies. Here, CTLA4 is linked to complement deficiency.