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  3. The Gene Variation Causes an Autism Common genetic variations that can contribute to autism have been reliably identified fo

The Gene Variation Causes an Autism Common genetic variations that can contribute to autism have been reliably identified fo

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问题                  The Gene Variation Causes an Autism
    Common genetic variations that can contribute to autism have been reliably identified for the first time in research that promises to improve the diagnosis and understanding of the disorder. The DNA changes, which affect genes involved in early brain development, are together involved in up to 15 percent of autism cases, the most extensive study of its kind yet conducted has found. The findings significantly deepen scientific understanding of the genetic origins of autism, offering insights into the condition’s underlying biology that could eventually lead to new treatment.
    While it has long been established that autism has a strong inherited component, previous research has failed to reveal any common DNA variants that were involved. The new study has found a robust link between autism and six such variants. These do not invariably cause the condition, but they are about 20 percent more common in children with autism than they are in those who are unaffected. The results are especially significant because the variants lie between two genes, called CDH9 and CDH10, which are known to play an important role in forming nerve connections in the brain.
    Hakon Hakonarson, of the Children’s Hospital of Philadelphia in the United States, who led the research, said: " Because other autism researchers have made intriguing suggestions that autism arises from abnormal connections among brain cells during early development, it is very compelling to find evidence that mutations in genes involved in brain interconnections increase a child’s risk of autism". This comprehensive research opens the door to more focused investigations into the causes of autism disorders. It moves the field of autism research significantly ahead, similar to the way oncology research progressed a few decades ago with the discovery of specific genes that give rise to cancers.
    In the study, the research team compared the DNA of 3,100 individuals from 780 American families each with at least two autistic children. The scan was then repeated in a group of 1, 200 people with autism and nearly 6, 500 unaffected controls. This revealed six genetic variants that were significantly more common in the autistic group. All were on chromosome five, and appear to affect the CDH9 and CDH10 genes. The CDH9 and CDH10 genes affect the way that nerve cells in the brain communicate with one another, which is thought to be a problem in autistic spectrum disorders (ASD). Autism involves a characteristic triad of symptoms: impairments in social and communication skills, as well as repetitive behavior and/or narrowly restricted interests. It is estimated that as many as one in 150 people have a disorder on the autistic spectrum.
What does "All" (Line 9, Para. 4) refer to?
选项 A、The autistic children.
B、The unaffected controls.
C、The autistic group.
D、The six genetic variants.
答案D
解析 语义分析题。根据上下文判断，可以很容易看出“All”这里指代的是前一句话中的宾语“six genetic variants”，即患有自闭症的病人体内更常见的六种基因变体。
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