If an expectant father is experiencing even mild stress when his baby is conceived, it could negatively affect the brain development of the child in the womb because of damage to his sperm, new research on mice has revealed.

When it comes to mothers, scientists have long-known that factors, such as poor diet, stress or disease, can negatively affect a child's development during pregnancy. This can partly be explained by the fact that environment can actually affect the functioning of certain genes based on a field of study known as epigenetics.

However, the influence of a father's environment is not understood to the same degree. Neuroscientist Tracy Bale, from the University of Maryland, presented her findings at the 2018 annual meeting of the American Association for the Advancement of Science, on 16 February.

In her previous research, Bale has found that male mice experiencing prolonged periods of mild stress tend to have offspring with a reduced response to stress – a condition which has been linked to various disorders, including depression and post-traumatic stress disorder.

Bale and her team identified the cause of this reduced stress response in the offspring, tracing it to changes in genetic material known as microRNA in the father's sperm. This molecule plays a key role in determining which genes become functional proteins.

For the new research, which is yet to be published in an academic journal, the scientists further investigated the male reproductive tract – known as the caput epididymis – and the changes affecting the microRNA.

In the caput epididymis there are structures where sperm matures that release tiny vesicles – small, fluid-filled sacs – which are filled with microRNA. These vesicles can fuse to sperm, altering its genetic material. However, when the father is stressed, these vesicles become damaged, which negatively affects the sperm.

These findings indicate that even seemingly innocuous environmental factors affecting fathers can have a significant impact on the development and health of future offspring.