Natural history, immunological and genetic characteristics of preclinical inflammatory bowel disease (EARLY): study protocol for a prospective cohort study.

Background: The period prior to the diagnosis of inflammatory bowel disease (IBD), defined as the preclinical phase, has emerged as a potential target for disease modification strategies. Despite the relevance of an early diagnosis to the prognosis of the disease, only a limited number of patients are diagnosed during this window of opportunity. Objectives: To determine the risk of developing symptoms after an incidental diagnosis of IBD and to describe the clinical, genetic, and immunological characteristics of IBD during its preclinical phase. Design: This study protocol describes a prospective, multicenter cohort study in which incidental (i.e., asymptomatic) IBD within the colorectal cancer screening program will be characterized from a clinical and multi-omic perspective and compared with symptomatic patients and healthy non-IBD controls. Methods: Samples from blood, urine, stool, and intestinal endoscopic biopsies will be obtained at baseline. A second sample set will be obtained after 52 weeks from those who remain asymptomatic; samples will also be obtained in those with new-onset symptoms. Medical treatment will be prescribed in all patients following current guidelines. Follow-up visits will be performed every 6 months for 10 years, and all new-onset symptoms, changes in disease behavior, extraintestinal manifestations, IBD-related medical therapies, or surgeries will be recorded. Two control cohorts will be included: one including recently diagnosed symptomatic IBD patients (<3 months), and another with healthy non-IBD controls after a normal ileocolonoscopy, in whom samples will be obtained at baseline. Samples from patients and controls will undergo genetic, proteomic, transcriptomic, single-cell RNA sequencing, metabolomic, and microbiome analyses, and integration of data between the different omic perspectives will also be performed. The study has been approved by the Basque Country Ethics Committee (PI2021116). Conclusion: EARLY will generate a unique dataset addressing a previously unexplored area of IBD, with the final aim of describing the prognosis of patients from its earlier phases on the disease and integrating clinical and omic data into useful tools for the long-term prediction of disease outcomes. Trial registration: NCT05698745.