CTLA4 and immune system disorder: These genetic disorders, such as Cytotoxic T-Lymphocyte-Associated Protein 4 (CTLA-4) [21,22], haploinsufficiency [22,23], autoimmune lymphoproliferative syndrome (ALPS), and common variable immunodeficiency (CVID), offer insight into the complex immune dysfunctions that may underlie ITP and often feature refractory or atypical courses of thrombocytopenia [24,25].