新闻周刊:非洲基因对癌症研究很重要(3)（在线收听）

The Perils of Exclusion

排除在外的风险

Including Africa in the search for problematic SNPs has several crucial advantages.

包括非洲在内，寻找有问题的单核苷酸多态性有几个关键的优势。

SNPs involved in diseases like cancer are usually rare, and a rare SNP found in the genome of someone with cancer could lead a researcher to link the two.

与癌症等疾病相关的SNP很罕见，在癌症患者的基因中发现罕见的SNP可让研究人员将这两者联系起来。

But what seems like an uncommon mutation among European genomes may turn out not to be when Africans are added to the mix, says Nicola Mulder, who analyzes genetic data at the University of Cape Town in South Africa.

但是，在欧洲基因中看似罕见的突变当加入非洲基因时，可能并不罕见了，南非开普敦大学分析基因数据的尼古拉·穆德如是说。

That mistake could waste years of effort and lots of money.

那个错误可能会浪费多年努力和大量金钱。

A group of scientists once presumed that five genetic variants caused a dangerous thickening of the heart, even going so far as to tell people with those variants that their DNA put them at risk for cardiac troubles.

一组科学家曾假设五种基因变异造成危险的心脏增厚，甚至告诉那些有变异的人其DNA可能会导致他们有心脏问题风险。

But they were wrong.

但他们错了。

Those five variants were not rare at all and in fact completely harmless.

这五种变异一点都不罕见，且事实上是完全无害的。

If the scientists had included African populations in their work, they might have known.

如果科学家已经把非洲基因囊括进了其研究中，那么他们可能已经意识到了这个问题。

More important, compared with Europeans and Americans, Africans have much better genomes for research, again because of their ancestral age.

更重要的是，和欧洲人、美洲人相比，非洲人有更多可研究的基因，这又是因为他们的祖先处在更早的年代。

Over time, as a genetic material is handed down from one generation to the next, SNPs tend to gather in clusters, making them easier for researchers to find.

随着时间的推移，随着遗传物质从一代传到下一代，SNP倾向于聚集成簇，使得研究者更容易找到它们。

As a consequence, they are more apparent in older genomes—in other words, African ones.

因此，它们在更古老的基因组中更为明显——换句话说，是在非洲。

"That can be of use to all populations," says Tishkoff.

“这对所有人群都有用，”蒂什科夫说。

For example, this clustering phenomenon led geneticists to a gene associated with LDL cholesterol (the bad kind) and another related to inflammation.

例如，这种聚类现象导致基因学家发现了一种与低密度脂蛋白胆固醇(一种有害的胆固醇)有关的基因，另一种与炎症有关。

African genomes have been rubbing up against environmental threats for far longer than any others, forcing the appearance of some surprising traits that may hold vital clues about disease.

非洲基因对抗环境威胁的时长要大于其他地方的基因，这就形成了某些可能意想不到的性状，可能是治疗某些疾病的重要线索。

A genetic mutation that enables us to survive one hazard may also shackle us with a less harmful new trait.

一种能使我们在恶劣环境下存活的基因变异，可能会带给我们有些小伤害的新性状。

Take sickle cell anemia: The gene behind this condition also protects against malaria.

以镰状细胞贫血为例：导致这种疾病的基因也能预防疟疾。

Another mutation makes people immune to the parasite behind African sleeping sickness but also increases their risk of kidney disease.

另一种变异让人们对导致非洲昏睡病的寄生虫免疫，但也增加了患肾病的危险。

It's not hard to imagine, Tishkoff notes, a mutation that enabled people to survive some menace but also left them predisposed to cancer.

蒂什科夫称，不难想象，人类因这种变异在某些威胁下生存下来，但也因此易患癌症。

Though the menace disappeared—say, in the move from East Africa to North America—the variant remained.

尽管这种威胁消失了，比如从东非到北美的迁移，但这种基因变异仍然存在。

These relic mutations could help explain how or why cancer evolved.

这种遗留下来的突变可能会帮助解释癌症是怎样或者说为什么演变的。

"Given the vast genetic variation that exists in African genomes," Rotimi says,

“鉴于非洲基因组存在巨大的基因变异，”罗蒂米说，

"it is likely that we can find genetic variants that are important to cancer that may not be discovered from other human populations."

“很可能我们可以找到对癌症很重要的基因变异，而这种变异可能不会在其他人群中被发现。”

And just as African genomes can help us recover our collective past, they can also save us from a perilous future.

正如非洲的基因组可以帮助我们找回我们共同的过去一样，也可以把我们从危险的未来中拯救出来。

Some genetic abnormalities influence how our bodies respond to medications, a field known as pharmacogenomics.

一些基因异常会影响我们的身体对药物的反应，这是一个被称为药物基因组学的领域。

One variant, for example, leaves people with HIV less tolerant to an anti-retroviral drug, a discovery that is changing treatment regimens across sub-Saharan Africa.

如，有种变异使艾滋病毒感染者对抗逆转录病毒药物的耐受性降低，这一发现正在改变整个撒哈拉以南非洲地区的治疗方案。

Another messes with the breast cancer drug tamoxifen.

另一种药物与乳腺癌药物他莫西芬有关。

The more diverse the genome, the higher the odds of finding mutations that may shape the choice of medication.

基因组多样化越大，发现决定药物选择的基因变异的几率越大。

"Increasing genomic research in Africa is going to benefit not just people of African descent," Tishkoff says, "but all people."

“在非洲不断增加基因组研究将不仅造福于非洲后裔，” 蒂什科夫称，“而且对全人类有益。”