The 12 km de la Trisomie 21 takes place in November in Chauray, Deux-Sèvres, western France. It features a 12 km adult run, children’s races, and 6 km or 12 km walks. Trisomie 21 Deux-Sèvres organizes the event annually, with the 12 km distance referencing Trisomy 21. The start is typically at the Trévins sports complex, with walkers beginning before runners and children's events later. Participants are encouraged to wear green, and a portion of each entry fee supports research.
The course combines town streets, paved roads, paths, and the Sèvre riverbanks. It includes ascents, turns, and accelerations, making it a varied route. Walkers follow the same course as runners but in reverse. One past edition, following a two-year health-crisis hiatus, saw 350 runners and 200 hikers. Benoit Boutet led from the start and ran solo for the entire 12 km, navigating muddy sections. Sophie Steunou was the leading woman in that event, participating for the first time.