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From the passage, you may infer that most people______.
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Several studies have proven that fish intake can lower the mortality rate due to coronary
What is the most important condition when bone marrow transplantation is used to restore the immune system of certain patients？
Countless people are born with(生来就具有某种特点)the susceptibility to inherit a genetic disease. But scientific progress, especially the art of interfering with(干涉,阻碍) the genetic makeup of the human body, has helped doctors prevent more and more inherited disorders in the last decade.
Dr. Thomas Caskey of the Baylor University College of medicine in Houston, Texas, is a pioneer in molecular biology(分子生物学). Through the techniques of genetic engineering(基因工程), he transfers genes from one organism to another. Caskey uses a certain type of virus, called a retrovirus(逆转录病毒), as the vehicle for the gene transfer. He first cripples the virus by removing the portion it needs to reproduce itself. The crippled virus becomes harmless while still being able to deliver a cargo to its destination.
The cargo in Caskey's experiment is the human A-D-A gene, taken from bone marrow. A-D-A stands for(代表) adenosine deaminase(腺苷脱氨酶), an important component of the human immune system. A defect in the A-D-A gene leads to immune deficiency, rendering(致使) the body defenseless against infections. Caskey's purpose was to see if the human A-D-A gene could repair the defective immune system of a mouse.
In the experiment the mouse was given a dose of radiation heavy enough to destroy its immune system. The animal next was injected with the crippled virus carrying the human A-D-A gene. According to Caskey, "the mouse will die within 10 to 14 days unless a successful transfer of bone marrow cells takes place. So we lethally irradiate and subsequently rescue the mouse by bone marrow transplantation(骨髓移植)with the cells that have been infected with the virus." The mouse now carries the human gene that salvaged its immune system.
Bone marrow transplantation has an established place in contemporary medical practice. Employed to restore the immune system of certain cancer patients and of people who have been exposed to radiation, bone marrow transplantation works only if there is a good match between donor and recipient.
The procedure would be much easier if bone marrow were like blood. People with type O blood are universal donors(万能供体). Their blood may be transfused to those who have different blood types. Unfortunately, there is no such thing as a universal bone-marrow type. Researchers may have found a way, however, to overcome this problem. The solution, if it works, would be to implant the patient with his own, perfectly matching(型配), bone marrow.
The idea, as Caskey explains it, is to "correct the patient's disease with his own ceils, but those cells have added to them a normally functioning gene. "In other words, surgeons would take defective bone-marrow cells from the patient and put them into a laboratory dish where the cells would be exposed to a crippled virus carrying a healthy AD-A gene from a donor. The A-D-A gene would repair the defective cells and then the cells would be reinjected into the patient. Thus, in Caskey words, "the patient would be transplanted by his own ceils containing the added normal gene."
The technique sounds deceptively(靠不住地) simple. In reality, though(可是,不过, 然而), it is complex. A number of laboratories have tested various intermediate steps of the process, but, according to Caskey, "no single laboratory has put together the entire technology successfully, and highly reproducibly, to proceed with a gene transfer at-tempt in man."
For some time now, the U.S. National Institute of Health has been taking a close look at(仔细,研究) the effectiveness and safety of the procedure, as well as the ethical questions it raises. There doesn't seem to be much concern about the ethics of gene transfer into a human being to correct a genetic defect.
Dr. W. French Anderson of N. I. H. wrote recently that "claims that new organs, designed personalities, master races, or Frankenstein(佛兰肯思泰因，一个创造怪物而自己被它毁灭的医学研究者，英国女
The study deals with the intake(摄影) of n-3 fatty acids and fish. The researchers calculated the intake of fish for 44,895 male health professionals—most of them dentists—in 1986 and kept track of their health status for the next six years. Surprisingly, the intake of n-3 fatty acids or fish in 1986 was not related to the risk of subsequent coronary disease. The number of participants was much larger than in other studies, and the methods and data analysis were solid. Also, measurements of fatty acids in adipose tissue showed that the questionnaire reliably ranked respondents according to their intake of 3 fatty acids.
The researchers carefully spell out the limitations of the study. First, two thirds of the men had greatly increased their intake of fish over the 10 years before 1986. Some of those increases could have occurred. Shortly before the base-line investigation in 1986, because the inverse relation between fish consumption and mortality due to coronary heart disease was first reported in 1985. Thus, data on fish intake may not reflect long term habits, and changes in fish intake during follow-up could also have attenuated an association with coronary disease. The authors performed separate analyses including only men who reported no change in their fish intake and again found no effect. However, it is hard for people to recall whether they changed their diet several years ago.
Second, the fish intake of these educated men was high and was more comparable with that of Norwegians or Japanese than with intake in the U.S. men studied previously. The epidemiologic data suggest that any beneficial effect is obtained with one or two servings of fish per week and that more is not better. Moreover, previous studies of fish intake have shown an association with the rate of mortality due to coronary disease, rather than with the incidence of nonfatal coronaty disease or coronary surgery. When seen in that light, there is some agreement between the present study and previous reports, because the risk of death from coronariy heart disease was about 25 percent lower among men who ate at least some fish than among those who ate no fish at all.
A third limitation of the study was that some of the men studied may have begun to eat fish, or may have eaten more, because they thought that they were at increased risk of a heart attack;the men in the highest 20 percent of the study group in terms of their in-take of n-3 fatty acids more frequently reported a family history of coronary disease or a personal history of high cholesterol levels than men who ate less fish.
The Harvard investigators concluded that increasing fish intake beyond one or two servings per week is unlikely to reduce the risk of coronary events substantially in men who are initially free of coronary disease. This is a prudent conclusion, and it could be extended to fish-oil capsules, which provide n-3 fatty acids in much larger amounts than are commonly consumed in food.
The findings of the Health Professionals Follow-up Study should somewhat dampen enthusiasm for fish and fish oil as a panacea against coronary disease. A little fish may still do some good, but more fish is not necessarily better.
Good diet helps prevent coronary heart disease.
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