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  3. Some scientists have concluded that narcolepsy, a disease which disrupt

Some scientists have concluded that narcolepsy, a disease which disrupt

游客2024-01-12  71
问题          Some scientists have concluded that narcolepsy, a disease which disrupts
     sleep patterns, arises when unknown agents in the environment spur an
     autoimmune reaction winding up damaging neurons in the brain circuits that
     control arousal and muscle tone. Honda found that all members of a group of
(5)   narcoleptics had one aspect of their tissue type in common, one of the human
     leukocyte antigens (HLAs). Whereas the HLA type was clearly not sufficient to
     induce narcolepsy, Honda’s finding indicated that HLA type greatly affected
     susceptibility to the disease. HLA molecules are pitchfork-shaped structures that
     cells of the body use to show pieces of the proteins they contain to the immune
(10)  system, which ordinarily attacks foreign substances and cells infected by
     viruses.
         Evidence for an autoimmune cause of narcolepsy will most likely come from
     studies of the brains of people who had the disorder. Ever since Gineau
     correctly named narcolepsy as a distinct syndrome in 1880, researchers have
(15)  examined the brains of patients in a futile search for neurological damage that
     could explain the symptoms of the disease. Mignot observed that the brains of
     narcoleptic dogs had more than the usual number of receptors for the
     neurotransmitters acetylcholine, dopamine and norepinephrine and higher levels
     of some of the neurotransmitters themselves, changes identical to those Aldrich
(20)  later noted human narcoleptic brains.
         Given that narcolepsy is not progressive but chronic—i.e. after the
     establishment of symptoms, narcoleptics do not deteriorate or improve—
     pathologists may have been focusing their efforts on the wrong stage of the
     disease’s progression. This suggested that the damage might occur during a
(25)  short time, roughly during the period in which a patient first develops signs of
     the illness. Debris left over from degenerative processes that occurred at the
     age of 20 would be removed by the brain’s support cells long before most
     patients died, and any remaining clues would be obscured by the normal
     degeneration of aging. As a loss of neurons would be undetectable unless the
(30)  dead cells were concentrated in a particular area, as in Parkinson’s disease, or
     unless many neurons died, as in Alzheimer’s disease, I therefore examined the
     brains of narcoleptic dogs shortly after their symptoms had begun, and found
     clear evidence that neurons in certain areas of the dogs’  brains were
     degenerating between one and two months of age, just before and during the
(35)  onset of symptoms. Evidence of the degeneration largely disappeared by the
     time the dogs were six months old. At this moment, all we can give patients are
     drugs to treat narcolepsy’s symptoms, even though this research promises the
     definite potential of a cure.
选项 A、presenting a hypothesis and describing compelling evidence in support of it
B、raising a question and describing an important discovery that led to an answer
C、showing that a certain autoimmune disease cannot yet be treated effectively with drugs
D、explaining what evidence exists for an autoimmune cause for narcolepsy
E、discussing the importance of research on animals for the study of human disease
答案 D
解析
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