Taken together, our analysis of GP130 p.R281Q clearly demonstrate that this variant (I) causes a selective defect in IL-11 signaling due to a decrease in GP130–IL11RA interaction, (II) occurs in an evolutionary conserved region of the protein, (III) is associated with craniosynostosis in one of two human subjects, and (IV) causes facial synostosis in a mouse model. Here, IL6ST is linked to craniosynostosis.