MAGICEvidence of Abnormal Fecal Microbiota in Healthy Subjects at High Risk for Crohn's Disease: Family Studies and Relations With a Particular Genetic Profile and Serological. Comparison of Affected Individuals, Their Siblings and Healthy Controls.

Crohn's disease is a chronic inflammatory bowel disease associating flares and remission periods. Its etiology is unknown and there are no specific therapy. CD affects young patients and has a major impact on quality of life. There are few population-based studies and there are about 2.5 million affected patients in Europe and North America. From data from EPIMAD Registry the number of affected patients in France should be 200 000. The Crohn's disease pathogenesis is bad known; It coul be the results of the activation of the gastro-intestinal immune system toward gut microbiota in genetically susceptible hosts. In CD patients there is an important ecologic modification of the flora with an excess of Bacteroidetes and Proteobacteria and a decrease of anti inflammatory bacteria (Firmicutes). In ileum of CD patients a specific E Coli (adherent and invasive E Colo) is found in two thirds of cases.The presence of this AIEC seems to be associated to the variant NOD2 (results from our team in multiplex families). In a family with at least 1 patient with CD, the healthy first degree relatives present a high risk (\* 10) to also develop a CD. The primary objective is the comparison of microbiota between patients with CD, healthy controls non genetically linked and first degree healthy relatives of patients with CD. The first endpoint is the Lachnospiraceae rates in each group. The secondary objectives are : 1. the search for an association between bacterial dysbiosis and different genetic backgrounds in patients with CD, their first degree healthy relatives and controls. 2. the quantification of potential invasive bacteria with invasive properties (E. coli including adherent-invasive E. coli, Shigella, Salmonella, Yersinia, Campylobacter), and fecal fungal flora (Candida albicans, in particular) and their association with genetic and serological profiles in patients with CD, their healthy relatives and control subjects. 3. a study of environmental risk factors using a questionnaire to be submitted to CD patients, their healthy relatives and control subjects.