科学家发现与自闭症相关的基因突变

Three new studies have uncovered extremely rare genetic mutations that shed new light on the potential environmental and biological roots of autism, a brain disorder that causes social and developmental delays in children, beginning at a young age. Scientists say the DNA glitches found in a small subset of autistic children were not inherited by them, but occurred spontaneously at their conception, increasing their risk for developing the disorder.

三项新的研究发现了极其罕见的基因变异，开启了对自闭症的潜在环境因素和生物学基础的新认识。自闭症是一种因脑部受损而导致儿童社交及发育延迟，它从婴幼儿时期就开始显现出来。科学家说，在一组自闭症儿童身上发现的DNA异常并不是来自遗传，而是在怀孕时自然产生的，这种异常增加了这些儿童发展成自闭症的风险。

One study found that having the rare genetic mutations could increase by 5 to 20 times a child's risk of developing autism spectrum disorders. These disorders range from mild cognitive delays and developmental impairments such as Asperger's syndrome to profound social dysfunctions and repetitive behaviors. Autism is being diagnosed, on average, in one of every 88 children in the United States, according to a recent government estimate.

一项研究发现，罕见的基因突变可能使儿童出现自闭症系列障碍的风险增加5到20倍。这些障碍包括从轻度的认知延迟和发育缺陷，比如阿斯伯格综合症，到严重的社交功能障碍和重复某种固定的行为。根据政府最近公布的一项数据，在美国，每88名儿童中估计就有1名自闭症患者。

Another study turned up biological evidence to support previous observations that the mutations are four times more likely to originate in male DNA than in the female DNA, and are more likely to appear in children of middle-aged and older fathers than in those of fathers younger than 35. Researchers speculate that the frequent turnover in a male's sperm cells increases the chance for errors in the genetic copying process. When a parent transmits such a transcription error to his offspring, the result can be a genetic mutation in the child that can cause autism. But researchers stress the risk of getting one of these badly-copied genes is extremely small.

另一项研究发现了支持之前观察所得结论的生物学证据，那就是，男性DNA发生相关变异的可能性比女性高出四倍。而且年龄大于35岁的父亲生出的孩子比小于35岁的父亲生出的孩子更可能发生这种基因突变。研究人员猜测，产生男性精子的细胞经常翻转，使得基因复制过程中出错的可能性增加。当父亲将这样的转录错误传给他的孩子，就可能导致孩子出现基因变异，从而造成自闭症。不过研究人员强调，出现这种复制出错的基因的可能性极小。

The mutations, also called "de novo" mutations, are spontaneous abnormalities that scientists say are distributed widely across the genome of affected children. They account for a very small percentage of diagnosed cases of autism, a diverse family of disorders with a variety of suspected genetic and environmental causes.

这种变异，也称为自发性突变(denovo)，是指自然发生的异常。科学家说，这种异常在受影响儿童的基因组中广泛存在。这种变异在自闭症病例中只占很小一部份，更多的自闭症病例据信是由各种各样的遗传和环境因素造成的。

Mark Daly of the Center for Human Genetics at the Broad [BROH-de] Institute at Harvard University and the Massachusetts Institute of Technology, led one of the studies. Daly says the the findings give autism researchers a starting point to better understand the biology of the disorder.

美国哈佛大学/麻省理工学院布劳德研究所人类遗传学中心的马克·达利领导进行了其中一项研究。达利说，这些发现可以让自闭症研究者开始更好地了解这种病症的生物学基础。

"So it doesn't explain all of autism and, in fact, more than half of the cases of autism don't have these types of mutations," said Daly. "But because they are very rare, they allow us to pinpoint when we see multiple kids with autism with mutations in the same gene."

达利说：“这并不能解释所有的自闭症病因，实际上，超过半数的自闭症病例并没有出现这种基因变异。但是由于这种变异非常罕见，因此我们可以精确确定这类自闭症儿童出现同一个基因变异。”

Scientists say there could be hundreds of mutated autism genes that code for proteins responsible for brain development. In the studies, all 549 children had the de novo mutations and their parents did not, allowing researchers to compare the genes of their children to that of their mothers and fathers, leading to the discovery of the DNA glitches.

科学家说，可能有数百个导致自闭症的突变基因，由这些基因编码的蛋白质负责脑部发育。在上述研究中，所有549名儿童都有自发性突变的基因，但他们的父母却没有。这样，研究人员将孩子的基因与他们父母的基因相比较，从而发现了DNA异常。