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

14 minute read
TIME

The remarkable advances in molecular biology during the past two decades have given man an understanding of the basic processes that shape his life and have placed within the realm of possibility medical achievements undreamed of a scant few years ago. As more and more of the once-mysterious life forces within the cell are defined in the logical language of chemistry, the way is being opened not only for permanent cures of genetic diseases but also for drastic changes in man’s genetic makeup. The acquisition of the power to eliminate genetic imperfections and engineer entirely new characteristics for humans is, for all of its promise, a frightening prospect for those who believe that man should not tamper with his inheritance. Yet even before the structure of DNA was defined and the genetic code broken, doctors had begun, mostly by trial and error, to develop techniques of genetic medicine.

Man today is heir to a host of inherited imperfections, ranging from diabetes to degenerative nerve disease. Each individual, geneticists have determined, carries between five and ten potentially harmful genes in his cells, and these flawed segments of DNA can be passed down to his progeny along with the messages that determine whether a child will have red hair or blue eyes.

Nature itself takes care of the worst genetic mistakes. One out of every 130 conceptions ends before the mother even realizes she is pregnant because the defective zygote, or fertilized egg, never attaches itself to the wall of the uterus. Fully 25% of all conceptions fail to reach an age at which they can survive outside the womb, and of these, at least a third have identifiable chromosomal abnormalities. Still, as many as five out of every 100 babies born have some genetic defect, and Nobel-Prizewinning Geneticist Joshua Lederberg believes the proportion would be even higher were it not for nature’s own process of quality control.

The most obvious deformities result from chromosomal abnormalities. Down’s syndrome, or mongolism, which occurs once in every 600 births, is caused when one set of chromosomes occurs as a triplet rather than a pair. Hydrocephalus, or water on the brain, and polydactyly, the presence of extra fingers or toes, also result from faulty genes.

But the majority of genetic stigmas have somewhat more subtle symptoms and occur when defective genes fail to order the production of essential enzymes that trigger the body’s biochemical reactions. Phenylketonuria (PKU) is caused by the absence of the enzyme necessary for the metabolism of the amino acid phenylalanine; as a result, toxins accumulate in the body and eventually cause convulsions and brain damage. Cystic fibrosis, which causes abnormal secretion by certain glands and respiratory-tract blockage that can lead to death by pneumonia, is the most common inborn error of metabolism; it is believed to be caused by a deficiency in a single gene.

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.

AT PRESENT, THE woman who learns through amniocentesis that she is carrying a seriously deformed fetus has only two choices: abortion or the heartbreak of delivering a hopelessly defective infant. But the mother whose unborn baby is found to have one of several hereditary enzyme deficiencies has a more acceptable alternative, for medicine has developed techniques for treating many such illnesses. An amniotic test for fetal lung maturity, for example, has helped warn doctors when a child may be born with hyaline membrane disease, which blocks proper breathing. In those cases, birth can be delayed by sedation until tests show the baby ready to breathe on its own. Tests that permit prompt postnatal detection of PKU give doctors an opportunity to place babies so affected on special diets that prevent the accumulation of the deadly toxins and allow them to live relatively normal lives.

Some treatments are even possible before birth. Physicians routinely perform intrauterine transfusions on fetuses suffering from Rh disease, a genetic condition that results from the incompatibility of maternal and fetal blood.

Artificial insemination, once the exclusive province of livestock breeders, also offers escape from some genetic mishaps. An estimated 25,000 women whose husbands are either sterile or carry genetic flaws have been artificially inseminated in the U.S. each year, many of them with sperm provided by anonymous donors whose pedigrees have been carefully checked for hereditary defects. Some 10,000 children are born annually of such conceptions.

Doctors also see possibilities in artificial inovulation, a procedure in which an egg cell is taken directly from the ovaries, fertilized in a test tube and then reimplanted in the uterus. By carefully scrutinizing the developing embryo in the test tube, doctors could spot serious genetic deficiencies and decide not to reimplant it, thus avoiding an abortion later on. If the embryo is normal, it could even be reimplanted in the womb of a donor mother and carried to term there, enabling the woman either unable or unwilling to go through pregnancy to have children that were genetically her own.

Even test-tube babies, once the stuff of science fiction, are now not only possible, but probable. Dr. Landrum Shettles of Columbia University and Dr. Daniele Petrucci of Bologna, Italy, have shown that considerable growth is possible in test tubes. Shettles has kept fertilized ova growing for six days, the point at which they would normally attach themselves to the lining of the uterus. Petrucci kept a fertilized egg alive and growing for nearly two months.

INDEED, ONLY development of an “artificial womb” capable of supporting life stands in the way of routine ectogenesis, or gestation outside the uterus, and now even this problem may yield to solution. Scientists at the National Heart Institute have developed a chamber containing a synthetic amniotic fluid and an oxygenator for fetal blood, and have managed to keep lamb fetuses alive in it for periods exceeding two days. Once their device is perfected, the baby hatchery of Aldous Huxley’s Brave New World will be a reality and life without birth a problem rather than a prophecy.

Man may eventually be able to abandon sexual reproduction entirely. That startling and perhaps unwelcome possibility has been demonstrated by Dr. J.B. Gurdon of Britain’s Oxford University. Taking an unfertilized egg cell from an African clawed frog, Gurdon destroyed its nucleus by ultraviolet radiation, replacing it with the nucleus of an intestinal cell from a tadpole of the same species. The egg, discovering that it had a full set of chromosomes, instead of the half set found in unfertilized eggs, responded by beginning to divide as if it had been normally fertilized. The result was a tadpole that was the genetic twin of the tadpole that provided the nucleus. Gurdon’s experiment was also proof of what geneticists have long known: that all of the genetic information necessary to produce an organism is coded into the nucleus of every cell in that organism.

Man, say the scientists, could one day clone (from the Greek word for throng), or asexually reproduce himself, in the same way, creating thousands of virtually identical twins from a test tube full of cells carried through gestation by donor mothers or hatched in an artificial womb. Thus, the future could offer such phenomena as a police force cloned from the cells of J. Edgar Hoover, an invincible basketball team cloned from Lew Alcindor, or perhaps the colonization of the moon by astronauts cloned from a genetically sound specimen chosen by NASA officials. Using the same technique, a woman could even have a child cloned from one of her own cells. The child would inherit all its mother’s characteristics including, of course, her sex.

Dramatic as cloning may be, it is overshadowed in significance by a technique that may well be practiced before the end of this century: genetic surgery, or correction of man’s inherited imperfections at the level of the genes themselves. When molecular biologists learn to map the location of specific genes in human DNA strands, determine the genetic code of each and then create synthetic genes in the test tube, they will have the ability to perform genetic surgery.

Some molecular biologists envisage using laser beams to slice through DNA molecules at desired points, burning out faulty genes. These would then be replaced by segments of DNA tailored in the test tube to emulate a properly functioning gene and introduced into the body as artificial—and beneficial—viruses.

THE CONCEPT IS not as farfetched as it sounds. Real viruses are merely segments of DNA (or RNA) surrounded by largely-protein sheaths; they penetrate the cell nucleus (leaving their sheaths behind) and take over the cellular DNA.

The potential of the technique is already being tested by an international research team in the treatment of two children whose hereditary inability to produce the enzyme arginase had resulted in severe mental retardation. The team infected the youngsters with a natural virus, the Shope papilloma, which contains DNA that triggers arginase synthesis. Although the experiment is expected to produce no improvement in the children’s mental condition, it may belatedly trigger the production of the missing enzyme and prove that viruses can carry beneficial messages to the cells.

There is other evidence that the beginning of genetic surgery is not far off. Dr. Sol Spiegelman of Columbia University has synthesized an artificial virus that is indistinguishable from its natural model and has used it to infect bacteria and produce new viruses. He and his colleagues have little doubt that they will also eventually create “friendly” viruses and use them to cure disease rather than cause it—by using the viruses to stimulate the production of the chemical products upon which health and life itself depend.

Prophylaxis is important, but man’s molecular manipulations need hardly be confined to the prevention and cure of disease. His understanding of the mechanisms of life opens the door to genetic engineering and control of the very process of evolution. DNA can now be created in the laboratory. Soon, man will be able to create man—and even superman.

Researchers have found that they can increase the life span of laboratory animals by underfeeding them and thus delaying maturation. This phenomenon, they believe, occurs because a smaller intake of food results in the formation of fewer cross linkages—connecting rods that link together and partly immobilize the long protein and nucleic acid molecules essential to life. If scientists can retard cross linking in man, they may well slow his aging process. Scientists also hope that they can some day do away with disease, genetically breeding out hereditary defects while breeding in new immunities to bacterial and other externally caused ailments. Finally, they look forward—in the distant future and with techniques far beyond any now conceived—to altering the very nature of their species with novel sets of laboratory-created genetic instructions.

Current predictions about the appearance of re-engineered man seem singularly uninspired. Some scientists argue that man’s head should be made larger to accommodate an increased number of brain cells. They do not, however, explain what man would do with this additional gray matter; there is good reason to believe that man does not use all that he presently possesses. A few others note that the efficiency of man’s hands could be increased by an extra thumb and his peripheral vision enhanced by protruding eyes—improvements that seem unnecessary in the light of man’s expanding technology.

SOME FAVOR LESS obvious alterations. They have suggested that man be given the genes to produce a two-compartment stomach (a cow has four) that could digest cellulose; that mutation could be advantageous if man fails to increase his food supplies fast enough to feed the planet’s growing population, but superfluous if he does. They also want man programmed to regenerate other organs, such as he now does with the liver, so that he can repair his damaged or diseased heart or lungs if necessary.

Others call for even more specialized humans to perform functions that in reality will probably be done better by machines. British Geneticist J.B.S. Haldane called for certain regressive mutations to enable man to survive in space, including legless astronauts who would take up less room in a space capsule and require less food and oxygen (larger and more powerful spacecraft would seem to be an easier and less monstrous solution). Haldane also suggested apelike men to explore the moon. “A gibbon,” he said only half-jokingly, “is better preadapted than a man for life in a low gravitational field.”

Eventually, scientists fantasize, man will escape entirely from his inefficient, puny body, replacing most of his physical being with durable hardware. The futuristic cyborg, or combination man and machine, will consist of a stationary, computerlike human brain, served by machines to fill its limited physical needs and act upon its commands.

Such evolutionary developments could well herald the birth of a new, more efficient, and perhaps even superior species. But would it be man?

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