<qa>  What is the primary aim of the study?The primary aim is to describe by principal component analysis and compare the gut microbiota between subgroups of paediatric-onset n75, elderly-onset CD patients n75 and control subjects 75 paediatric control and 75 elderly control subjects matched on age without an a priori approach of high throughput sequencing of bacterial DNA. As it has been shown that the type of IBD-associated dysbiosis depends on ileal involvement, Paediatric-onset and elderly-onset CD patients will be stratified according this parameter. 