Etiologically, the linkage of these defects to abnormalities in IL-6 and IL-11 signaling is supported by defects in GP130, which acts as a co-receptor for ligands including IL-6 and IL-11 upstream of STAT3 (Fig. 1), producing a syndrome that phenocopies aspects of STAT3-HIES including recurrent infection, skeletal abnormalities, and raised IgE [10]. Here, STAT3 is linked to infection.