单选题 Parkinson"s disease, first described in the early 1800s by British physician James Parkinson as "shaking palsy", is among the most prevalent neurological disorders. According to the United Nations, at least four million people worldwide have it; in North America, estimates run from 500,000 to one million, with about 50,000 diagnosed every year. These figures are expected to double by 2040 as the world"s elderly population grows; indeed, Parkinson"s and other neurodegenerative illnesses common in the elderly (such as Alzheimer"s and amyotrophic lateral sclerosis) are on their way to overtaking cancer as a leading cause of death. But the disease is not entirely one of the aged: 50 percent of patients acquire it after age 60; the other half are affected before then. Furthermore, better diagnosis has made experts increasingly aware that the disorder can attack those younger than 40.
So far researchers and clinicians have found no way to slow, stop or prevent Parkinson"s. Although treatments do exist-including drugs and deep-brain stimulation-these therapies alleviate symptoms, not causes. In recent years, however, several promising developments have occurred. In particular, investigators who study the role proteins play have linked miscreant proteins to genetic underpinnings of the disease. Such findings are feeding optimism that fresh angles of attack can be identified.
As its 19th-century name suggests--and as many people know from the educational efforts of prominent Parkinson"s sufferers such as Janet Reno, Muhammad Ali and Michael J. Fox--the disease is characterized by movement disorders. Tremor in the hands, arms and elsewhere, limb rigidity, slowness of movement, and impaired balance and coordination are among the disease"s hallmarks. In addition, some patients have trouble walking, talking, sleeping, urinating and performing sexually.
These impairments result from neurons dying. Although the victim cells are many and found throughout the brain, those producing the neurotransmitter dopamine in a region called the substantia nigra are particularly hard-hit. These dopaminergic nerve cells are key components of the basal ganglia, a complex circuit deep within the brain that fine-tunes and co-ordinates movement. Initially the brain can function normally as it loses dopaminergic neurons in the supstantia nigra, even though it cannot replace the dead cells. But when half or more of these specialized cells disappear, the brain can no longer cover for them. The deficit then produces the same effect that losing air traffic control does at a major airport. Delays, false starts, cancellations and, ultimately, chaos pervade as parts of the brain involved in motor control--the thalamus, basal ganglia and cerebral cortex--no longer function as an integrated and orchestrated unit.

单选题 Which of the following statements about Parkinson"s disease can be best supported by the passage?

单选题 The author of the passage suggests that the developments in the study of Parkinson"s disease can help______

单选题 According to the passage, what causes Parkinson"s disease?

单选题 Janet Reno and Michael J. Fox are mentioned in the passage because______

单选题 The primary purpose of this passage is to______