Vehicle door with a window and a window pane guide comprising an element to avoid the twisting of the guide

The door has a hollow lower caisson mounted on a frame that receives a window pane sliding inside a vehicle and retractable in the caisson, where the frame has two struts with slides. A bracket (32) reinforces one of the struts and includes an attachment (40) for fixing a horizontal unit (42) which is integrated to a lower end of a guide. Outer and inner vertical panels delimit the caisson.