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Science and Technology Epigenetics and stress Baby blues
科技 外因遺傳與壓力 新生兒藍調曲
A mother's stress while she is pregnant can have a long-lasting effect on her children's genes
母親孕期壓力過大會對孩子的基因造成長期影響
RESEARCHERS have known for years that children whose mothers were chronically stressed during pregnancy—by famine, anxiety, the death of a relative or marital discord, for instance—show higher-than-normal rates of various psychological and behavioural disorders when they are adults.
研究人員多年前就發現，如果母親在懷孕期間長期遭受因饑餓，焦慮，親友死亡或婚姻不幸等引起的過大壓力，她們的孩子成年后出現各種心理疾病和行為問題的幾率會高于平均幾率。
They have also known for a long time that those brought up in abusive environments often turn out to be abusive themselves.
研究人員也早知道，在受虐環境下成長起來的孩子長大后往往本身也有施虐傾向。
The second of these observations is usually put down to learning.The reason for the first has remained unclear.
人們通常把后面的這個發現歸咎于盲目效仿，而頭一個發現的原因卻仍舊模糊不清。
A study just published by Axel Meyer, Thomas Elbert and their colleagues at the University of Konstanz in Germany, however, points to a phenomenon called epigenetics as the likely answer.
然而，德國康士坦茨大學的Axel Meyer, Thomas Elbert以及他們的同儕們最近發表的研究報告指出，一種被稱為"外因遺傳"的現象很有可能就是這個問題的答案。
And if Drs Meyer and Elbert are right, it also suggests an alternative explanation for the inheritance of abusiveness.
如果Meyer和Elbert博士的結論是正確的，那它也為施虐遺傳現象做出了另一個解釋。
Epigenetics is a type of gene regulation that can be passed from a cell to its daughters. The most common mechanism is methylation.
外因遺傳是一種可以傳給下一代細胞的基因調控過程，
This attaches methyl groups (a carbon atom and three hydrogens) to either adenine or cytosine,
最常見的方式是通過甲基化作用來完成，該作用可以讓甲基（由一個碳原子和三個氫原子組成）附著于腺嘌呤或胞嘧啶上。
two of the four chemical bases that form the alphabet of DNA, depending on the gene involved.
腺嘌呤和胞嘧啶是DNA四大成分其中之二，而到底附著于哪一個則取決于具體的基因。
The consequence is to inactivate the gene being methylated.
甲基化作用將使甲基化的基因失去活性。
In the case of stress, previous studies have suggested that methylation of the gene which encodes glucocorticoid receptors is important.
以往的研究表明，當母親壓力過大時，負責為糖皮質激素受體編碼的基因的甲基化具有重要意義。
Glucocorticoid receptors relay signals from stress hormones in the blood into cells.
糖皮質激素受體依靠血液中的壓力激素發出信號而進入細胞。
In particular, they do so in those regions of the brain that control behaviour.
尤其值得注意的是，這個過程在大腦中控制人體行為的區域進行。
Newborns whose mothers suffered from depression while they were pregnant are known to have more highly methylated glucocorticoid-receptor genes than others.
新生兒的母親若是在懷孕期間出現抑郁癥狀，他們糖皮質激素受體基因的甲基化程度就會比其他新生兒更高。
The same is true of children who were abused when young.
幼時受虐的孩子在這一點上也有相同表現。
In infants, the level of glucocorticoid-receptor methylation is correlated with the release, in response to stress, of higher-than-normal amounts of stress hormones.
胎兒糖皮質激素的甲基化程度與人體抑郁時分泌過多的壓力激素有關。
And in rats, such methylation makes young animals especially sensitive to stress, and also fearful of novelty.
而老鼠試驗表明，這樣的甲基化過程讓幼小動物對壓力尤其敏感，對新鮮事物也感到恐懼。
What has been unclear until now, however, is how long such effects persist.
然而，現在還沒弄清楚的是，這樣的效應會持續多久。
Dr Meyer's and Dr Elbert's study, published in Translational Psychiatry, offers a clue.
Meyer博士和Elbert博士在《轉化精神病學》雜志中發表的研究報告給出了答案。
Troubled teens
問題青少年
Their team examined the methylation of the glucocorticoid-receptor gene in a group of children ranging in age from ten to 19 years, and in those children's mothers. The researchers also used a psychological survey to try to determine which of the mothers had been physically or psychologically abused before, during or after pregnancy.
他們的研究小組對一組年齡從10歲到19歲不等的青少年以及他們母親體內糖皮質激素受體基因的甲基化程度進行了測量，還通過心理測試試著找出哪些母親在孕期中或者生產后曾遭到身體或者心理上的虐待。
They found that women abused during pregnancy were significantly more likely than others to have a child with methylated glucocorticoid-receptor genes.
研究發現，孕期中遭到虐待的母親生下糖皮質激素受體基因被甲基化的幼兒的可能性要比其他母親高出得多。
By contrast, abuse before or after pregnancy resulted in no such correlation. Nor was the mother's own methylation affected by violence towards her.
相反，在孕前或是生產后遭到虐待的母親則不會生下這樣的幼兒，而且她們本身基因的甲基化與否也跟是否遭到家庭暴力無關。
Taken together, these results suggest that glucocorticoid-receptor-gene methylation happens in the fetus in response to a mother's stress, and persists into adolescence.
總體看來，這些結論表明胎兒糖皮質激素受體基因的甲基化是由于母親壓力過大引起的，并且其影響將會持續到青春期。
This has implications for those adolescents' long-term health.
這會影響青春期孩子的長期健康。
Dampened glucocorticoid-receptor-gene activity has been shown to increase the risk of obesity, of depression and of some autoimmune diseases. It also makes people more impulsive and aggressive—and therefore,
事實證明，糖皮質激素受體基因不夠活躍會增加孩子患肥胖癥，抑郁癥以及某些免疫系統疾病的風險，也會讓他們成年后個性更加沖動，更加富有侵略性。
if male, more likely to abuse the pregnant mothers of their children, thus perpetuating the whole sorry cycle.
因此，如果孩子是男性，他們更有可能施虐于懷著自己孩子的待產婦女，從而造成持續的惡性循環。
Why, in light of such negative effects, have humans evolved to be programmed this way while still in the womb?
發現了這種消極效應后，科學家們不禁問道，為何人類還在子宮內的時候就被設立了這樣的一個進化程序呢？
Part of the answer is probably that not all the negative consequences would have shown up at the time the mechanism was evolving.
也許部分原因是，當甲基化作用還在進化的時候所有的消極影響不會當即全部表現出來。
Obesity, for example, is rare in a state of nature.
例如肥胖癥在極少數情況下是天生的。
The other part is that some of the consequences probably have a positive effect.
還有一個原因是，部分消極影響也許會帶來積極效應。
If a mother lives in an environment where fear-inducing experiences are common, say, giving her offspring a sensitivity to fear may be no bad thing.
如果母親生活在一個很容易產生害怕心理的環境里，那么讓她的后代對害怕情緒敏感也許并不是壞事。
What can be done with such knowledge is unclear.
知道了這些真相對人們有什么意義尚不明確。
Drugs that demethylate DNA are under development, but are still some way from approval—and, in any case, interfering with epigenetics, which is a widespread mechanism of gene regulation, is a drastic approach.
讓DNA反甲基化的藥物還在研發中，并且還未通過臨床證明。另外，外因遺傳是基因調控的常見手段。從任何角度來說，干預外因遺傳都是一種極端激進的做法。
The research might, though, point to the period when intervening to stop abuse will have the greatest effect.
但這項研究也許會把科學家們引向另一個方向，那就是找出對基因調控進行干涉從而阻止家庭暴力的最有效時期。
Then again, such intervention is always desirable, for the sake of both mother and child.
為了讓母親和孩子們都幸福，這樣的干涉乃眾望所歸。
