The risk of having a child with Down Syndrome increases as the mother gets older. For women under the age of 30, the rate is about one in 1,000 and for women of the age of 44, it rises to one in 35. The rise of Down Syndrome children born to older women may happen for several reasons. Males produce sperm throughout their life, while a woman is born with all the eggs she will ever have. The egg remains in a state of incomplete development until the process of ovulation begins. If a woman is 40 years old, that means she has a 40 year old egg. The eggs in older women may be past their prime or over the years have been exposed to damaging influences such as medication, radiation or other harmful influences. Until recently , the mother was thought to be providing the extra genetic material. Researchers have found that in about 25 percent of the cases, the father was the one to provide the extra genetic material. (Down Syndrome "The Psychology of Mongolism" pg. 4).
Types of Down Syndrome.
Trisomy 21 is the most common form of Down Syndrome representing about 95 percent of all the cases. Trisomy 21 is the presence of three chromosomes rather than the normal pair of chromosomes designated as 21. Trisomy 21, results from an error in cell division during the development of the egg, sperm, or during fertilization. (Genetic Disorder Source Book pg. 5).
Translocation is the interchange of chromosomes or parts of chromosomes which may result in a mismatched pair. Children with translocation Down Syndrome have an extra number 21 chromosome which has broken and become attached to another chromosome. In some cases a person can carry a broken chromosome 21 without showing any symptoms of Down Syndrome because they have the correct amount of genetic material, even though some of it is out of place. Translocation only occurs in about 4 percent of Down Syndrome Cases. (Genetic Disorder Source Book).
