Childhood trauma leaves a lasting mark 鈥� in your sperm. A study of 28 men has found that those who had difficult childhoods carry chemical clues to their past in their sperm, and these may be passed down to their sons.
Previous studies have found that stress can affect the health and behaviour of mice, and that these changes seemed to be passed down to their offspring, possibly through their sperm. Such transgenerational changes have been controversial. While we know that fathers who smoke tend to have heavier sons, and people whose grandparents experienced famine may live longer, it鈥檚 still unclear how such environmental factors could have lasting effects down the generations.
One way that this might happen is via microRNAs 鈥� short molecules that can affect how genes work 鈥� that are passed to the next generation in sperm. To investigate this, of Tufts University, Massachusetts, asked male donors at a fertility clinic to complete a standard survey that assesses childhood traumas, including physical abuse and parental divorce. People who turn out to have experienced four or more of the stressors on the survey list are known to have a higher risk of health problems, including depression and heart disease.
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Changing sperm
When Feig鈥檚 team analysed the men鈥檚 sperm, they found that those who scored 4 or above on the survey had less of two different types of microRNAs in their sperm. The function of these two microRNAs is not yet known, although in general, microRNAs are thought to play an important role in development while in the womb.
The two microRNAs that were reduced in the men with difficult childhoods are only ever found in sperm, not in eggs, so a mother cannot provide backup if her partner鈥檚 sperm is lacking in these molecules. 鈥淭his is the first time that any kind of stress has been shown to change human sperm,鈥� says Feig.
The team found that stressful environments also caused the same two microRNAs to decline in the sperm of mice. When these mice reproduced, their male offspring also showed a low level of these microRNAs in their sperm, suggesting that stress has a lasting effect that can be passed through generations.
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Assessing trauma
鈥淭he results are extremely compelling,鈥� says , at the University of Utah, although she says it will be difficult to test what long-term impacts these reduced microRNAs have on people.
Feig hopes that signs of childhood trauma like sperm microRNAs may be useful for doctors or perhaps for screening people who want to join the military. As well as raising health risks, childhood trauma can also make people more vulnerable to developing post-traumatic stress disorder. While questionnaires can assess childhood stresses, people can lie to avoid stigma, or because their memories fail.
, of the University of Massachusetts Amherst, says the most important implication of Feig鈥檚 findings is that, after years of focusing on the mother鈥檚 role in conception and pregnancy, 鈥渄ad鈥檚 do matter鈥�.
Read more: Old fathers pass on more mutations to kids than old mothers
