BDNF and proctitis: In contrast, no significant interactions of smoking quantity GRS with smoking were observed for surgery in UC patients.42 However, BDNF (rs6265) significantly interacted with smoking for proctitis in UC patients.42 In addition, the interaction between CHRNA5 (rs16969968) and smoking in UC (OR = 2.72, Pinteraction =.05) seems more prominent than in CD for the risk of surgery within a differtent cohort, while no interaction effect was seen for time to surgery.43