Currently, no cures exist for any of the syndromes caused by chromosomal abnormalities. For many of these conditions, the age of the mother carries an increased risk for giving birth to a child with a chromosomal abnormality. The risk for Down syndrome, for instance, jumps from 1 in 1,000 when the mother is age 15-30 to 1 in 400 at age 35, increasing risk with increasing maternal age. One theory postulates that this is due to the build-up of toxins over time within the ovaries, damaging the egg cells that are present in females since early childhood. By the time they are ovulated after age 35, the chances of fertilization of a damaged egg are greater.
People at high risk for these abnormalities may opt to know whether the fetus they have conceived has one of these abnormalities. Amniocentesis is a procedure in which some of the amniotic fluid that surrounds and cushions the fetus in the uterus is sampled with a needle placed in the uterus. The amniotic fluid contains some of the fetus's skin cells, which can be tested for chromosomally-based conditions. Another test, called chorionic villi sampling, involves taking a piece of tissue from a part of the placenta. If a chromosomal defect is found, the parents can be advised of the existence of the abnormality. Some parents opt to abort the pregnancy; others can prepare before birth for a child with special needs.
In addition to amniocentesis and chorionic villi sampling, researchers are working on devising easier tests to detect certain abnormalities. A new test for Down syndrome, for instance, measures levels of certain hormones in the mother's blood. Abnormal levels of these hormones indicate an increased risk that the fetus has Down syndrome. These enzyme tests are safer and less expensive than the sampling tests and may be able to diagnose chromosomally-based conditions in more women. Most recently, scientists have devised a procedure called in situ hybridization which uses molecular tags to locate defective portions of chromosomes collected from amniocentesis. The process uses fluorescent molecules that seek out and adhere to specific faulty portions of chromosomes. Chromosomes having these faulty regions then "glow" (or fluoresce) under special lighting in regions where the tags bind to, or hybridize with, the chromosome. The procedure makes identification of defects easier and more reliable.
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Brenda Wilmoth Lerner
Science EncyclopediaScience & Philosophy: Chimaeras to ClusterChromosomal Abnormalities - Normal Number And Structure Of Human Chromosomes, Normal Cell Division, Alterations In Chromosome Structure, Genetic Counseling - Alterations in chromosome number