Special Section: THE BODY: From Baby Hatcheries To Xeroxing Human Beings

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Most people are unaware that they are carrying defective genes until they have a deformed, diseased or mentally retarded child. While medical science has not yet developed the techniques for repairing the bad genes, it can increasingly determine that they are present. Genetic counselors can thus advise prospective parents on the possibilities that their offspring will be born with genetic diseases. Properly informed, a couple that runs a high risk of producing a defective child may well decide to forgo having children.

If both parents carry genes for diabetes, for example, the chances are one in four that their children will inherit an increased risk for developing the disease. If either parent actually suffers from diabetes, the odds are even worse. Members of one large South Dakota family afflicted with a rare degenerative nerve disease have been advised, for example, that the odds are 50-50 that any children they have will suffer loss of balance and coordination and die, probably of pneumonia, by age 45 (TIME, Jan. 25).

Genetic counseling once relied more heavily on mathematics than medicine to predict the chance of hereditary handicaps. But it is now possible for doctors to identify and catalogue chromosomes. If there are certain chromosomal abnormalities, the prospective parents are informed that they will almost definitely produce deformed offspring. While this knowledge may take some of the mystery and romance out of procreation, it also eliminates much of the uncertainty. As one geneticist puts it, "There is nothing very romantic about a mongoloid child or a deformed body."

An even more important technique enables physicians to examine the cells of the unborn only months after conception and to determine with accuracy whether or not the infant will inherit his parents' defective genes. The procedure is known as amniocentesis, from the Greek amnion (membrane) and kentesis (pricking); it is performed by inserting a long needle through the mother's abdomen and drawing off a small sample of the amniotic fluid, the amber liquid in which the fetus floats. Physicians then separate the fetal skin cells from the fluid and place the cells in a nutrient bath where they continue to divide and grow. By examining the cells microscopically and analyzing them chemically, the doctors can identify nearly 70 different genetic disorders, most of them serious.

Amniocentesis, performed between the 13th and 18th weeks of pregnancy, is not without some risk to both mother and baby. But in cases where family history leads them to suspect genetic defects, physicians feel that the benefits more than justify the danger; for the tests, which have been carried out on more than 10,000 women in the U.S. alone in the past 40 years, have proved extremely accurate. Using amniocentesis, Dr. Henry Nadler, a Northwestern University pediatrician, diagnosed mongolism in ten of 155 high-risk pregnancies tested. Subsequent examination of the fetuses showed that his diagnosis was correct in all cases.