儿童受虐待可能改变大脑基因表现——表观遗传学
本帖最后由 原军超 于 10-9-28 22:03 编辑
研究显示儿童受虐待可能改变大脑基因表现
研究人员对自杀人群的尸检显示，儿童早期遭受虐待的经历可能会永远改变大脑的基因表现。
据英国《新科学家》周刊网站７日报道，目前科学界普遍认为，遗传基因及其开启和关闭方式共同决定人类自身的发展。大多数基因控制开关在我们出生前就已存在，但也有规模较小的控制开关在人的整个生命过程中形成。当ＤＮＡ中的甲基增多时，基因就会关闭。研究表明，饮食、压力甚至母爱等外部因素都能影响基因表现。
加拿大麦基尔大学的摩西·西夫指出，约７０％的自杀者在早期都有遭受虐待或无人照管的经历。他和同事研究了曾在早期无人照管或遭受虐待的１３名自杀者的大脑，他们对大脑中被称为海马的部分尤为感兴趣。海马负责记忆和情绪，曾经遭受虐待的人，海马的体积较小。
研究人员检测了负责控制ＲＮＡ的海马基因（ＲＮＡ生成蛋白质)。他们将检测结果与１１名年龄和性别相同、成长经历正常、但死于非命的实验对象进行对比后发现，自杀者海马基因关闭的比率要高得多，这表明他们的海马确实不太活跃。
西夫表示，下一步就要证明甲基化水平的改变是童年遭受虐待的结果，并非由自杀本身造成。为此他正在对没有遭受虐待的自杀者进行研究。
下面是从英文网站上找到的对同一研究结果的报道：
Childhood victims may carry chemical changes to DNA into adulthood
London, February 23 (ANI): A new study conducted by researchers of McGill
University in Montreal, Canada, has shown that childhood abuse victims can carry
chemical changes to their DNA into adulthood.
Study leader Michael Meaney, a neurobiologist at the university, says that the
research team observed that suicide victims with childhood abuse history were
more likely to carry such chemical changes in their DNA as could affect their
ability to respond to stress as adults.
He revealed that people without childhood abuse history did not show the same
pattern of DNA modification, and had normal expression of NR3C1, a gene linked
to stress responses.
However, Joan Kaufman, a psychologist at Yale School of Medicine in New Haven,
Connecticut, who was not involved in the new study, said that the findings
should not be taken to suggest that the effect of childhood abuse is indelible.
“The long-term effects of early abuse are not inevitable, and the more you
understand about the mechanisms of risk, the more you can devise treatments,”
Nature magazine quoted her as saying.
The current research builds on animal studies that showed that rat pups that are
stressed because they were raised by negligent mothers have extra methyl groups
in their DNA in a region of the genome that controls expression of Nr3c1, the
equivalent gene in rats.
The researchers point out that such ”methylation” can reduce gene expression.
NR3C1 encodes a protein expressed in neurons that responds to hormones called
glucocorticoids. Lower expression of NR3C1 could be harmful because reduced
responses to these glucocorticoids have been linked to increased stress.
With a view to seeing whether or not the results of animal studies translated
into humans, Meaney and his colleagues collected brain samples from the Quebec
Suicide Brain Bank.
They looked at samples from 12 suicide victims with a history of childhood
abuse, 12 suicide victims with no history of childhood abuse, and 12 controls
who had died suddenly from other causes.
The researchers revealed that people with a history of childhood abuse had lower
levels of glucocorticoid receptors than those who had not been abused or had not
committed suicide.
According to them, childhood-abuse victims had a similar methylation pattern to
that seen in rats that had been stressed as pups.
Meaney, however, added that since his team have not yet looked for effects on
egg or sperm DNA, it was doubtful that the changes could affect the germline.
The researcher also said that it was yet to be determined whether trauma as an
adult produces the same pattern of changes.
Martin Teicher, director of the Developmental Biopsychiatry Research Program at
Harvard Medical School in Belmont, Massachusetts, says that there may be times
during childhood when the developing brain is particularly responsive to abuse.
His team imaged the brains of women who had been victims of child abuse, and
found that those abused between the ages of three and five, or eleven and
thirteen, had a smaller hippocampus a region in the brain that is important for
memory and learning than those who had not been abused2.
With an eye on searching a way out, the researchers carried out studies on mice,
and fould that the methylation changes could be reversed: if pups reared by
negligent mothers are later treated with a chemical that removes DNA
methylation, their stress responses return to normal.
However, presently, such drugs are not ready for use in humans, and could carry
unwanted side effects.
But medication may not be the only way to treat victims of child abuse, for
psychotherapy has been shown to produce chemical changes in the brain, and might
be able to reset the methylation pattern, says Meaney.
“A social event got you into it. Could a social event get you back out? That’’s
a very viable hypothesis,” he said.
A research article on these findings has been published in the journal Nature
Neuroscience. (ANI)
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