Down syndrome is a condition of mental retardation and associated physical disorders caused by an extra chromosome. Each person has 23 pairs of chromosomes, one pair from each parent. A person with down syndrome has a 3rd chromosome on the 21st pair. The results are both mental and physical, and often include small eyes, and hands, protruding tongues, short necks and fingers. There are all different levels of the disorder, and the probability of a child being born with it increases as the mother's age increases; this is especially true as the mother becomes middle aged.