Science and Babies Private Decisions, Public Dilemmas (1990) / Chapter Skim
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6. Progress in Research
6. Progress in Research
Pages 126-146
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From page 126... ...
In this chapter are described three examples of research areas that hold much promise: the role of the brain in reproduction, new methods of diagnosing genetic diseases, and research on embryo health. ROLE OF THE BRAIN TN REPRODUCTION Research makes it clear that the brain governs most aspects of reproductive functioning.
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From page 127... ...
In some mammals, including humans, the hypothalamus integrates information about body weight, stress, exercise, and overall health. If these inputs indicate that a female is well nourished and able to sustain the stress of pregnancy and lactation, the hypothalamus secretes gonadotropinreleasing hormone in regular pulses, and regular ovulatory and menstrual cycles begin.
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From page 128... ...
At present, this treatment is available from medical centers only for primary amenorrhea; approval for treatment of other forms of the disorder is expected from the Food and Drug Administration by late 1990. Not all scientists agree about the importance of keying the changes in the pulsing rate exactly to those that occur naturally, but they do agree that the critical feature in the reproductive hormone network is the delivery of GnRH into the blood circulation in small regular bursts.
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From page 129... ...
What remains to be known is the exact morphologic and physiologic nature of this neuronal system: what starts the firing, what controls its duration, and what stops it as abruptly as it began. DIAGNOSING GENETIC DISEASES The increasing ability of medical scientists today to diagnose genetic disorders is making it possible for more couples who may carry the genes for an inherited disease to give birth to healthy babies.
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From page 130... ...
Credit: National Institute of Child Health and Human Development On the horizon are techniques for examining embryos before they are artificially implanted for chromosomal abnormalities and defective genes. If procedures to diagnose genetic and chromosomal defects in early-stage embryos are developed successfully, couples at risk for passing on a genetic disease could be offered in vitro fertilization as a way to have a healthy child.
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From page 131... ...
This rarely occurs in a heterogeneous population, but in small closed societies where there is a lot of intermarriage, the odds are substantially increased and a gene mutation can eventually become quite prevalent. Today a number of inherited diseases are associated with certain ethnic groups.
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From page 132... ...
Like genetic tests, prenatal tests are done on an individual basis when parents fear their offspring might be born with a serious disability or fatal illness. For some diseases, however, technology makes broad screening programs of adults and newborns possible.
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From page 133... ...
For some of the most common, however, such as Down syndrome and certain neural tube defects, prenatal tests do exist. The majority of these prenatal tests depend on biochemical assays to detect the evidence of a genetic disease.
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From page 134... ...
Fetal blood testing involves drawing blood from the umbilical cord via a needle guided by ultrasound through the mother's abdomen. Fetal blood can be tested for infectious diseases, for evidence of abnormal metabolism, and for defective genes that account for blood diseases such as thalassemia, sickle cell disease, hemophilia, and chronic granulomatous disease, a disorder that affects males, making them very vulnerable to bacterial infections.
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From page 135... ...
The study found that in experienced hands the spontaneous abortion rate for chorionic villus sampling is 0.S percent higher than for amniocentesis. Ultrasound technology has vastly improved since its debut in the 1970s, and, in the hands of an experienced physician with a good knowledge of fetal anatomy, it is a useful diagnostic tool.
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From page 136... ...
Fetal liver cells are not collected by amniocentesis, fetal blood sampling, or chorionic villus sampling. However, because all cells carry all the genes of a particular individual, PKU and a continually growing number of other genetic diseases—can be diagnosed prenatally by using DNA analytical techniques to examine fetal skin or blood cells.
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From page 137... ...
Dr. Caskey notes that new technologies being used to distinguish the genetic mutations for Lesch-Nyhan syndrome also make it possible to detect with great efficiency the many deletions that can occur in the extensive Duchenne muscular dystrophy gene.
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From page 138... ...
In a Swedish study of infertile women undergoing ovulatory stimulation, a team led by Dr. Hakan Wramsby found that nearly 50 percent of the eggs recovered were abnormal.
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From page 139... ...
Investigators in England reported early in 1989 that they had removed single cells from 30 three-day-old embryos and had successfully tested the cells for a gene sequence found only on the male-determining Y chromosome. The research demonstrated that it was possible to diagnose genetic diseases in embryos, and it is expected that the test for gender will be useful to women who carry the genes for male-linked diseases such as Duchenne muscular dystrophy, hemophilia, and Lesch-Nyhan syndrome.
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From page 140... ...
Moreover, couples at risk for giving birth to a child with a hereditary disease could use embryo testing and in vitro fertilization as a way to have a healthy baby a more desirable alternative to becoming pregnant, testing the fetus, and facing the prospect of having an abortion if the fetus inherited the disease. Observers believe research on embryos is likely to lead to more wanted and healthy children and to a reduction in the number of abortions.
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From page 141... ...
To transfer them all to the mother's uterus could result in a multiple pregnancy, which often is hazardous to the mother as well as to the fetuses. Research has demonstrated that embryos not transferred to the uterus during in vitro fertilization can be preserved by freezing and storing, ready to be used if the first embryo transfer is not successful.
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From page 142... ...
Improving Embryo Development Most of the culture media used to nourish eggs and embryos in IVF centers are based on media developed for mouse eggs. If there are significant differences in metabolism between a human egg and a mouse egg, a culture medium tailored more closely to the needs of the human ovum might improve the results of in vitro fertilization.
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From page 143... ...
Until the ethical concerns about such studies are addressed in the United States and guidelines developed, there will be no federally funded, organized program for basic embryo research. For carriers of genetic diseases who want to have children and for infertile couples for whom IVF treatment fails, the lack of a policy regarding embryo research means a substantial delay in medicine's ability to help them have healthy children.
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From page 144... ...
couples at risk for having a child with a hereditary disease could be offered embryo testing and in vitro fertilization as a way to have a healthy child. In another approach toward solving infertility problems, researchers are finding that important aspects of reproductive functioning are governed by the brain.
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From page 145... ...
1989. The safety and efficacy of chorionic villus sampling for early prenatal diagnosis of cytogenetic abnormalities.
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From page 146... ...
1988. Chromosomal analysis of human oocytes and embryos in an in vitro fertilization program.
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