The contribution of IL-11 to STAT3-HIES’s skeletal phenotype is supported by mutations in IL11RA causing an overlapping syndrome of craniofacial abnormalities without immunodeficiency [75], demonstrating how phenocopies caused by mutations along the STAT3 axis have shaped understanding of cytokine:phenotype correlation in STAT3-HIES. This evidence concerns the gene STAT3 and Immunodeficiency.