Among the novel IEIs recently described include 3 reports describing 9 individuals from 7 independent kindreds with severe primary immunodeficiency disease (PID) due to loss-of-function (LOF) mutations in the NCKAP1L gene encoding the actin regulatory protein hematopoietic protein-1 (Hem1) (2–4). The gene discussed is NCKAP1L; the disease is inborn error of immunity.