GDNF and Crohn disease: Although all specimens studied from patients with DD were obtained from histologically un-inflamed areas showing no evidence for abscess formation, transmural inflammatory infiltrates nor fibrotic scarring, it cannot be excluded that recurrent inflammation might have contributed to alterations of the GDNF system in DD, as it has been previously shown that GDNF levels are modified in inflammatory bowel diseases (e.g. ulcerative colitis, Crohńs disease, infectious colitis) [26].