Understanding Down Syndrome: Trisomy 21 Explained

Down syndrome (DS), also called Trisomy 21, is a condition in which extra genetic material causes delays in the way a child develops, both mentally and physically. Normally, at the time of conception a baby inherits genetic information from its parents in the form of 46 chromosomes: 23 from the mother and 23 from the father. In most cases of Down syndrome, a child gets an extra chromosome 21 — for a total of 47 chromosomes instead of 46. It is this extra genetic material that causes the physical features and developmental delays associated with DS (kidshealth.org). Trisomy 21 is one of the most common human chromosomal aberrations, occurring in about one out of every eight hundred live births. Major characteristics of DS include: delayed mental

However, studies have demonstrated that cells in a state of meiosis are particularly sensitive to environmental influences such as viruses, x-rays, and cytotoxic chemicals. It is possible that environmental influences may play a role in nondisjunction events (Arlene, 2014). Scientists and researchers are now aware that there is a correlation between the mother’s age at the time of conception and the risk of having a baby born with DS, most would argue that the older the mother, the higher the chances are. Studies comparing the chromosomes of the affected offspring with those of both parents have shown that the nondisjunction event is maternal about 75 percent of the time. This maternal age effect is thought to result from the different manner in which the male and female gametes are produced. Gamete production in the male is a continual, lifelong process, while it is a one-time event in females (Arlene, 2014). A woman 's chances of giving birth to a child with Down syndrome increase with age because older eggs have a greater risk of improper chromosome division. By age 35, a woman 's risk of conceiving a child with Down syndrome is about 1 in 350. By age 40, the risk is about 1 in 100, and by age 45, the risk is about 1 in 30