Heterozygous NFKB1 gene mutations cause common variable immunodeficiency (CVID)149,150 while NFKB2 gene defects have been shown to be associated with B cell dysregulation in patients with common variable immunodeficiency (CVID) or combined immunodeficiency (CID)151 Among phenocopies of IEI, somatic, GOF STAT5b mutation in a hematopoietic progenitor has been recently reported in 2 patients with a novel syndrome of nonclonal eosinophilia, atopic dermatitis, urticarial rash, and diarrhea.152. Here, STAT5B is linked to combined immunodeficiency.