ARPC1B deficiency is an AR form of CID associated with immune dysregulation and platelet abnormalities.92, 93, 94 The Actin-Related Protein Complex 1B (ARPC1B) is required for the assembly and maintenance of the ARP2/3 complex that plays a pivotal role in actin branching. The gene discussed is ARPC1B; the disease is combined immunodeficiency.