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DNA對疾病的預測能力有限

Study Says DNA’s Power to Predict Illness Is Limited
DNA對疾病的預測能力有限

If every aspect of a person’s DNA is known, would it be possible to predict the diseases in that person’s future? And could that knowledge be used to forestall the otherwise inevitable?

如果知道一個人DNA的全部內容,有可能預測出他將來會得什么病嗎?并且,能否以此來預防本來無法避免的事情?

The answer, according to a new study of twins, is, for the most part, “no.”

根據一項有關雙胞胎的新研究,答案多半是“不能”。
 

While sequencing the entire DNA of individuals is proving fantastically useful in understanding diseases and finding new treatments, it is not a method that will, for the most part, predict a person’s medical future.

雖然個人全基因組測序在了解疾病和尋找新療法時已證明相當有效,但大多數情況下,它并不是能夠預測一個人將來健康狀況的方法。

So, the new study concludes, it is not going to be possible to say that, for example, Type 2 diabetes will occur with absolute certainty unless a person keeps a normal weight, or that colon cancer is a foregone conclusion without frequent screening and removal of polyps. Conversely, it will not be possible to tell some people that they can ignore all the advice about, for example, preventing a heart attack because they will never get one.

這項研究的結論稱,因此,舉例來說,我們不可能說一個人必須保持正常體重,否則就一定會得II型糖尿??;也不可能說不經常篩檢并切除息肉就一定會得結腸癌。反之,我們也不可能對一些人說:因為他們永遠不會得心臟病,就可以罔顧一切預防心臟病發作的建議。

“The punch line is that this sort of personalized medicine will not in any way be the most important determinant of patient care,” said Dr. Bert Vogelstein of Johns Hopkins, who, with his colleagues and his son Joshua, analyzed the power of sequencing all of a person’s DNA to determine an individual’s risk of disease. The study, published online Monday in the journal Science Translational Medicine, involved data from 53,666 identical twins in registries from the United States, Sweden, Finland, Denmark and Norway. The registries included data on 24 diseases, telling how often one twin, both or neither got a disease.

約翰·霍普金斯大學的貝特·沃格爾斯坦(Bert Vogelstein)說:“這件事的好笑之處就在于,這種個性化的醫療無論如何也不是病人護理方面最重要的決定因素。”他和同事——也是他的兒子——約書亞(Joshua)一起,分析了個人全基因組測序對個人患病風險的預測能力。他們的研究于4月2號在線發表在《科學·轉化醫學》雜志網絡版上,包括了來自美國、瑞典、芬蘭、丹麥和挪威等國家所記錄的53666對同卵雙胞胎的數據。這些記錄里有24種疾病的數據,描述了同卵雙胞胎中的一人、兩人患病或者都不患病的機率。

Since identical twins share all of their genes, the investigators could ask to what extent genes predict an increased chance of getting a disease. Using a mathematical model, they reached an answer: not much. Most people will be at average risk for most of the 24 diseases.

因為同卵雙胞胎所有基因都相同,研究者們可以由此來研究基因能在多大程度上預測患病可能性的提高。他們采用數學模型得出的答案是:并不大。絕大部分人患上24種疾病中的絕大多數的風險都處于平均水平。

They asked: Would those who ultimately got one of the 24 diseases have been forewarned by DNA sequencing? “Unfortunately, it tells them they are at roughly the same risk as the general population,” said Dr. Vogelstein.

他們的問題是:那些最后得了這24種疾病中某一種的人,是否原本可以通過DNA測序來預警。沃格爾斯坦說:“很不幸,DNA測序表明,他們和普通人群的患病風險大體相當。”

The researchers also asked whether healthy people would learn by DNA sequencing that they were at low risk for a disease. Again, the results were disappointing. For example, more than 93 percent of women would learn they were at low risk for breast cancer and more than 97 percent of men and women would learn their risk for lung cancer was low. “But these negative tests do not mean they are at no risk for these cancers,” Dr. Vogelstein said. Their risk is more like that of the general population. And, Dr. Vogelstein says, even knowing you are at high risk for a disease may be less useful than it sounds. A woman who is at high risk for ovarian cancer might have a 10 percent risk, many times higher than average. That, Dr. Vogelstein said, “is unlikely to be the main determinant of her health.” But there was one positive finding — as many as 90 percent of people would learn that they are at high risk of getting at least one disease. And gene sequencing could, in theory at least, identify as many as 75 percent of those who will develop Alzheimer’s disease, autoimmune thyroid disease, Type 1 diabetes and, for men, heart disease.

研究人員還考查了健康人能否通過DNA測序來了解他們患某種疾病的風險較低。結果又一次令人失望。比如,超過93%的女性會了解到自己患乳腺癌的風險較低,而超過97%的男性和女性則會獲悉自己得肺癌的風險較低。沃格爾斯坦說:“但是,這種陰性測試結果并不意味著他們就沒有得這些癌癥的風險。”他們的風險和普通大眾更為接近。沃格爾斯坦還說,即使你知道自己患病風險高,可能也沒有聽上去那樣有用。一名卵巢癌高危女性或許有10%的風險,比平均值高許多倍,但沃格爾斯坦說,這樣“也不太可能成為她健康的主要決定性因素”。不過也有一個正面的發現——高達90%的人會通過DNA測序了解到他們處于至少患上其中一種疾病的高風險狀態。而且,至少從理論上講,基因測序可以發現多達75%的未來將患老年癡呆癥、自體免疫甲狀腺疾病和I型糖尿病的患者以及男性心臟病患者。

However, with the exception of heart disease, there is as yet no way to prevent these diseases or slow their progress. And since high risk of an infrequent disease, like ovarian cancer, is far from a prediction that the disease is in the person’s future, the information might be valuable but would not necessarily make much difference in the end.

然而,除了心臟病之外,對于其他這些疾病,目前尚無預防或延緩發病的方法。另外,由于罕見疾?。ㄈ缏殉舶┑母唢L險還遠無法被預測出一個人將來會得此病,這種信息或許會有價值,但最終未必會有什么幫助。

“The general point is absolutely correct,” said Dr. David Altshuler, professor of genetics and medicine at Harvard Medical School, who was not involved with the research. “Even if you know everything about genetics, prediction will remain probabilistic and not deterministic.”

并未參與該項研究的哈佛大學醫學院遺傳學及醫學系教授大衛·阿特舒勒(David Altshuler)說:“總體結論肯定是正確的。即使你知道了全部的遺傳信息,也只能預測概率而非確定性。”

The reason, he suspects, is that behavior, environment and random events tip the balance. “I am a big believer in randomness,” Dr. Altshuler said.

他推測,這是因為行為、環境和隨機事件起了決定性作用。阿特舒勒說:“我很相信隨機性。”

Dr. Vogelstein is too, but he had hoped the study might prove him wrong. He and his colleagues had studied a patient with pancreatic cancer. Several family members had also developed this rare disease, and so Dr. Vogelstein and his colleagues decided to determine the sequences of the patient’s genes, looking for a mutation.

沃格爾斯坦也有同樣看法,但他曾希望這項研究能夠證明自己是錯的。他和同事們一起研究了一名患胰腺癌的病人。該病人的幾名家族成員也都患有這種罕見疾病,因此,沃格爾斯坦和同事們決定測定該病人的基因序列來尋找突變。

“Indeed, we found the culprit,” Dr. Vogelstein said.

沃格爾斯坦說:“的確,我們找到了罪魁禍首。”

Several other research groups looked at families with other diseases and also found unexpected genetic culprits by sequencing all of a patient’s DNA.

其他幾個研究小組也通過病人的全基因組測序,查看了患有其他疾病的家族并發現了意想不到的遺傳致病原因。

“It occurred to us that maybe we could do this for everyone,” Dr. Vogelstein said. “Maybe we would find that most disease risk was concentrated in a relatively small number of people. That would have dramatic health policy implications. It would mean we could concentrate our surveillance on that proportion of the population that was at high genetic risk.”

沃格爾斯坦說:“這讓我們想到,或許我們可以對所有人進行測序?;蛟S我們會發現,絕大部分的疾病風險都集中在相對少數的人中間。這會對醫療政策有著很大意義。這意味著我們可以把疾病監控集中在高遺傳風險的那部分人群上。”

The twins study let him see what might be possible. And, he says, “it puts limits on what people might expect with this sort of testing.”

這項雙胞胎研究讓他看到了什么是可能的。他還說:“它對人們可能對這種測試所抱有的期待設定了限制。”

Other experts pointed out different aspects of DNA sequencing that can improve health and medical care. Sequencing can, in some cases, aid in determining a patient’s prognosis. It can find the causes of mystery ailments in individuals, and it can find mutations that appear to be driving the growth of cancers in individual patients.

另外一些專家指出了DNA測序能夠促進健康和醫療保健的另一些方面。在某些情況下,測序可以幫助確定病人的預后,也可以找出某些個體所患神秘疾病的原因,或找出單個病人中看來是在推動癌組織生長的突變。

Sequencing also is starting to help doctors decide who should take drugs to prevent diseases, as is happening with heart disease.

測序也開始幫助醫生決定哪些病人應該服藥來預防疾病,正如在心臟病治療中所做的那樣。

In heart disease, one pressing problem is how to decide which young and middle-aged adults would benefit from cholesterol-lowering statins to reduce the risk of a first heart attack, said Dr. Sekar Kathiresan, a genetics researcher who is director of preventive cardiology at Massachusetts General Hospital. The drugs reduce the risk by 20 percent, but if your risk is low to start with, a 20 percent reduction does not mean much.

馬薩諸塞州總醫院預防心臟病科主任、遺傳學研究員塞卡·凱西瑞山(Sekar Kathiresan)說,心臟病治療方面的一個緊迫問題是,如何決定哪些年輕人和中年人會受益于降膽固醇類藥物來降低首次心臟病發作的風險。這類藥物能將風險降低20%,但如果風險一開始就很低,降低20%也沒有太大意義。

Now, Dr. Kathiresan said, by analyzing data from studies that sequenced entire genomes, researchers have found 30 gene variants that, taken together, can identify healthy people who have twice the average risk of heart disease. “There is a great attraction to using genetics in this way,” he says.

凱西瑞山說,如今研究人員通過分析全基因組測序研究的數據,已經找到了30個基因變異,綜合起來,能夠確認出患心臟病風險是常人兩倍的健康人士。他說:“用這種方法使用遺傳學很有吸引力。”

Dr. Robert Cook-Deegan, professor of law, ethics and policy at Duke, notes that every person whose DNA is sequenced will get information about whether he or she will respond to certain drugs and whether certain side effects will result from taking certain drugs. Vanderbilt University is already doing genetic analyses of patients to help in prescribing a short list of drugs, says Dr. William Schaffner, chairman of the department of preventive medicine at its medical school.

杜克大學法律、倫理及政策系教授羅伯特·庫克迪根(Robert Cook-Deegan)指出,每一個接受DNA測序的人都可以得知某些藥物是否對他們有用,以及服用某些藥物是否會有特定的副作用。范德比爾特大學醫學院預防醫藥系主任威廉·夏夫那(William Schaffner)說,該校已經開始對病人進行遺傳分析,以幫助幾種藥物用于開處方。

But the real benefit of studying the human genome, Dr. Altshuler said, is not to predict people’s medical futures but instead to understand how diseases occur and to use that knowledge to develop better therapies. Already this sort of work has succeeded with an entirely new type of drug to lower levels of LDL, or “bad” cholesterol, he said.

不過,阿特舒勒教授說,研究人類基因組真正的好處不是為了預測個人未來的健康狀況,而是理解疾病是怎樣發生的,并利用這種知識來開發更好的療法。他說,這類工作已經成功地找到一種全新的藥物來降低LDL水平,即“壞”的膽固醇的水平。

“The reason we do it is because we want to use genetics to pry open the black box of how disease works,” Dr. Altshuler said. “Not to personalize existing treatments, but to develop new treatments that are more effective.”

阿特舒勒教授說:“這樣做的原因是,我們想用遺傳學來打開疾病如何發生的黑盒子。不是把現有的療法個人化,而是開發更加有效的新療法。”

And that, he said is “a work in progress.”

他說,那是“一項正在進行的工作”。
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