Down syndrome is a birth defect caused by a genetic disorder that affects 350,000 people in the United States. It is caused by genetic abnormalities and is not hereditary, which means that parents do not pass it on to their children. Genetics is the study of heredity, or how certain traits are passed from parents to children. Genes are the basic unit of heredity. Cells are the building blocks of our body, and each of us has more than 100 trillion cells. Our genes are found in chromosomes. Each cell in your body contains 46 chromosomes, or 23 pairs. In a person with Down syndrome there are 47 chromosomes. In 1956, a French researcher named Jerome Lejeune used a powerful new microscope to observe strands of human DNA. DNA is what contains an individual person's genes. He studied these DNA strands and determined that there is an extra strand on chromosome 21, which is now called “Trisomy 21” tri meaning three and somy for the word chromosome – meaning three chromosomes. No one knows exactly what causes Down syndrome, other than the fact that it is genetic. Many years ago, this condition was known as "Mongolism" or people who suffered from it were called "Mongolian idiots". But in later years, both Asians and the parents of these children protested these terms, and in the 1960s the condition became known as Down syndrome in honor of the English doctor John Langdon Down. Who, in 1866, studied people with mental retardation and noticed distinct physical characteristics in them. Some of the physical characteristics associated with Down syndrome are low muscle tone, many newborns appear floppy and untoned, have flat facial features, especially a small nose with a flattened bridge of the nose. Their eyes are slightly slanted with small folds of skin at the inner corner. They have a short neck, small, abnormally shaped ears and an enlarged tongue that often tends to protrude, making it difficult to understand speech. Many people with Down syndrome suffer from a variety of health problems. The most common and significant symptom is mental retardation, which varies from mild to moderate. People with Down syndrome suffer from congenital heart defects, which affect approximately 40-50% of these people. Their poor muscle tone makes physical activity difficult. There are many hormonal problems, mainly thyroid diseases. People with Down syndrome suffer from circulatory problems, respiratory disorders, ... middle of paper ... the placenta is removed and the cells are analyzed under a microscope for chromosomal abnormalities. The final test is amniocentesis, which is taking a sample of amniotic fluid from the uterus. This procedure is performed between the 14th and 18th weeks of pregnancy. This is the most reliable and accurate test. It is 99.8% reliable in testing for Down syndrome. There is another blood test available called percutaneous umbilical blood sampling (PUBS). The fact of the matter is that no matter how different or unusual these people appear, people with Down syndrome should be treated with respect and dignity just like you and me. These people are productive individuals and have many things to offer. Just because they are different doesn't mean they aren't valuable to us. We can learn patience and acceptance from them and until there is a cure, our acceptance and positive attitude will help us all move forward. Works Cited Diseases and Disorders - Down Syndrome, Christina M. Girod, San Diego, CA, 2001 Down Syndrome, Salvatore Tocci, Grolier Publishing Company, Inc., 2000www.aolsvc.health.webmd.aol.com/content/article /1680.54172www.my.webmd.com