科學家發現與自閉症相關的基因突變

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.

三項新的研究發現了極其罕見的基因變異，開啓了對自閉症的潛在環境因素和生物學基礎的新認識。自閉症是一種因腦部受損而導致兒童社交及發育延遲，它從嬰幼兒時期就開始顯現出來。科學家說，在一組自閉症兒童身上發現的DNA異常並不是來自遺傳，而是在懷孕時自然產生的，這種異常增加了這些兒童發展成自閉症的風險。

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.

一項研究發現，罕見的基因突變可能使兒童出現自閉症系列障礙的風險增加5到20倍。這些障礙包括從輕度的認知延遲和發育缺陷，比如阿斯伯格綜合症，到嚴重的社交功能障礙和重複某種固定的行爲。根據政府最近公佈的一項數據，在美國，每88名兒童中估計就有1名自閉症患者。

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.

另一項研究發現了支持之前觀察所得結論的生物學證據，那就是，男性DNA發生相關變異的可能性比女性高出四倍。而且年齡大於35歲的父親生出的孩子比小於35歲的父親生出的孩子更可能發生這種基因突變。研究人員猜測，產生男性精子的細胞經常翻轉，使得基因複製過程中出錯的可能性增加。當父親將這樣的轉錄錯誤傳給他的孩子，就可能導致孩子出現基因變異，從而造成自閉症。不過研究人員強調，出現這種複製出錯的基因的可能性極小。

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.

這種變異，也稱爲自發性突變(denovo)，是指自然發生的異常。科學家說，這種異常在受影響兒童的基因組中廣泛存在。這種變異在自閉症病例中只佔很小一部份，更多的自閉症病例據信是由各種各樣的遺傳和環境因素造成的。

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.

美國哈佛大學/麻省理工學院布勞德研究所人類遺傳學中心的馬克·達利領導進行了其中一項研究。達利說，這些發現可以讓自閉症研究者開始更好地瞭解這種病症的生物學基礎。

"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."

達利說：“這並不能解釋所有的自閉症病因，實際上，超過半數的自閉症病例並沒有出現這種基因變異。但是由於這種變異非常罕見，因此我們可以精確確定這類自閉症兒童出現同一個基因變異。”

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.

科學家說，可能有數百個導致自閉症的突變基因，由這些基因編碼的蛋白質負責腦部發育。在上述研究中，所有549名兒童都有自發性突變的基因，但他們的父母卻沒有。這樣，研究人員將孩子的基因與他們父母的基因相比較，從而發現了DNA異常。Thomas Lehner is head of genomics at the U.S. National Institute of Mental Health, which funded one of the studies. Lehner says the latest findings point researchers toward understanding the biological architecture of autism.

托馬斯·萊納是美國國立精神衛生研究所(NIMH)基因組研究部主管。該研究所資助了上述其中一項研究。萊納說，最近的這些研究成果將有望讓研究人員更好地瞭解自閉症的生物學基礎。

"And even better, we can design experiments that will help us get to point where we say, 'We are now able to understand a large proportion of the genetic variants - what we call a genetic liability - to autism,'" said Lehner.

萊納說：“更有甚者，我們可以設計一些試驗，這將有助於我們走向新的認識，那就是，我們將能在很大程度上了解與自閉症相關的基因變異，我們稱之爲致病基因的易患性。”

The latest studies give researchers new drug targets for treating autism. Mark Daly of the Broad Institute says scientists have seen promising results in animal studies.

最近的這些研究使研究人員確立了關於自閉症治療藥物的新目標。布勞德研究所的馬克·達利說，科學家在動物試驗方面看到充滿希望的研究成果。

"It's possible to reverse some of these symptoms in mice, even after the brain is developed," he said. "So it underscores that anything we think we know, we really are not sure of, as it pertains to diseases and disorders of the brain."

達利說：“甚至在腦部發育已經完成後，都有可能改變老鼠的一些症狀。因此，這表明，關於腦部疾病和異常，我們所認爲、所知道的任何事，其實我們並不確定。”

Scientists hope to identify many more autism genes within a few years.

科學家希望在幾年內發現更多的自閉症致病基因。

The three studies on the discovery of de novo genetic mutations in autism are published jointly in the journal Nature.

科學家希望在幾年內發現更多的自閉症致病基因。這三篇發現與自閉症相關的自發性基因突變的研究論文發表在《自然》雜誌上。