In humans, there are 23 pairs of chromosomes, which are all numbered. Sometimes there is an extra chromosome 21, or at least part of it. Although this may not seem like a big deal, this causes a common genetic disorder called Down syndrome. People with Down syndrome have many genetic deformities that result in abnormal phenotypes. Down syndrome is the major cause of mental retardation. However, the intensity of the effects varies among patients.
Besides mental retardation, many other side effects occur. There is a 30-50% chance of heart problems, a 10-12% chance of intestinal malformation, an increased risk for infections, and a 5-7% chance of gastroinintestinal tract disorders (digestive problems). The main occurrence of this is an obstruction of the upper part of the intestine, which can interrupt the digestive process and cause the baby to regurgitate food involuntarily.
There is an increased chance of ear infections, pneumonia, kidney disorders, thyroid disease, physical deformities, and weak muscles. As a baby, weak muscles are a major problem. They cause issues with crawling, walking, and development of motor skills. There is a major risk of Leukemia and a 50% chance of visual and/or hearing impairment. The disorder also causes a slow development rate. Many cases develop Alzheimer’s disease. Aging also causes these problems to increase in intensity. Because of these problems, the average life expectancy for this disorder is 35 years old.
There has been no proof of this disorder to be hereditary. It is the most common non-hereditary disorder; chances are about 1 in every 700 live births. The chance increases with the age of the mother. Women of 35 and older increase their chances to about 1 in 200. Women of 45 increase their chances to 1 in 30. Down syndrome is becoming more common, however, because women are having children later in life.
Being that it is not hereditary, the cause of Down syndrome is most...