It is possible that fibrosis in the inflamed esophagus of Nik−/− mice might occur through a TGFβ-independent mechanism, such as fibroblast growth factor 9 (FGF9), which is elevated in EoE patients (Mulder et al., 2009; Lucendo et al., 2011). The gene discussed is FGF9; the disease is eosinophilic esophagitis.