MODEL RELEASED. Down's syndrome. Woman with down's syndrome learning first aid during a British Red Cross demonstration. Down's syndrome is a genetic disorder caused by all or part of an extra 21st chromosome (one of the 23 pairs of chromosomes present in the human body). Individuals with the disorder tend to have lower than average cognitive abilities, such as learning disabilities. First aid training courses are among the many services offered by the British Red Cross. Photographed in the UK.