单选题 The last decade has seen a tremendous expansion of scientific knowledge in human genetics. Our understanding of human genes and of the genetic basis of disease has grown dramatically. Currently, more than 4, 000 diseases are known to be genetic and are passed on in families. Moreover, it is now known that alterations in our genes play a role in such common conditions as heart disease, diabetes, and many types of cancer.
The identification of disease-related genes has led to an increase in the number of available genetic tests that detect disease or an individual's risk of disease. New tests are being developed to detect colon cancer, breast cancer, and other conditions. Scientists are concerned not only that gene tests offered are reliable, but also that patients and health care professionals understand the limitations of such testing. The disclosure of test results could inflict psychological harm to a patient if safe and effective interventions are not also available.
Gene testing involves examining a person's DNA-taken from cells in a sample of blood or, occasionally, from other body fluids or tissues--for some anomaly that flags a disease or disorder. In addition to studying genes, genetic testing in a broader sense includes biochemical tests for the presence or absence of key proteins that signal aberrant genes.
The most widespread type of genetic testing is newborn screening. Each year in the United States, four million newborn infants have blood samples tested for abnormal or missing gene products. Some tests look for abnormal arrangements of the chemical bases in the gene itself, while other tests detect inborn errors by verifying the absence of a protein that the cell needs to function normally. Carrier testing can be used to help couples to learn if they carry--and thus risk passing to their children. Genetic tests-biochemical and DNA-based--also are widely available for the prenatal diagnosis of conditions such as Down syndrome.
Much of the current excitement in gene testing centers on predictive gene testing: tests that identify people who are at risk of getting a disease, before any symptoms appear. Tests are already available in research programs for some two dozen diseases, and as more disease genes are discovered, more gene tests can be expected.
Tests for a few rare cancers are already in clinical use. Predictive gene tests for more common types of cancer are still primarily a research tool, difficult to execute and available only through research programs to small numbers of people who have a strong family history of disease. But the field of gene testing is evolving rapidly, with new genes being discovered almost daily and innovations in testing arriving almost as quickly.

单选题 Scientists argue that the genetic testing is not perfect partly because ______.

单选题 The word "aberrant" in Paragraph 3 most probably means ______.

单选题 How does the newborn screening test work?

单选题 It can be learned from the last paragraph that ______.

单选题 The passage is intended to ______.