Father's nicotine use risks cognitive problems down the generations

A father's smoking habit can cause cognitive deficits in the second and third generations, a study in mice has shown.

Researchers studied the effects of nicotine on sperm DNA through three generations of mice. The study was the first piece of research showing that nicotine can affect the father's sperm.

'Our findings underscore the need for more research on the effects of smoking by the father, rather than just the mother, on the health of their children,' said Professor Pradeep Bhide, director of the Centre for Brain Repair at Florida State University College of Medicine and lead author of the study.

Male mice that were exposed to low-dose nicotine in their drinking water were bred with female mice who had never been exposed to nicotine. The researchers found that while the nicotine-exposed fathers behaved normally, the first-generation offspring was more likely to exhibit attention deficit, hyperactivity and cognitive inflexibility. When female, but not male, offspring from this generation were crossed with mice never exposed to nicotine, the second-generation offspring also displayed significant cognitive deficits, although at a lower level.

When the authors looked at the mice's genetic makeup they found that the males originally exposed to nicotine had epigenetic changes at certain locations of the DNA in their sperm. Such changes are associated with changing the level of expression of a gene. Some epigenetic changes can be reversed, but some can also be inherited by the next generation.

One of the genes affected was the dopamine D2 gene, which is important for brain development and learning. The D2 gene has been previously linked to behavioural disorders, such as attention deficit hyperactivity disorder (ADHD).

'Nicotine and cigarette smoke have been previously shown to cause widespread epigenetic changes. The fact that men smoke more than women makes the effects in males especially important from a public health perspective,' said Professor Bhide.

However, as the study was carried out in mice, the effects in humans may be complicated by many genetic and environmental differences.

Dr Susanna Roberts, a researcher at the Institute of Psychiatry Psychology and Neuroscience, King's College London, who wasn't involved in the study, said: 'Despite the interesting results, it is difficult to extrapolate the importance of these effects in humans, where the causal pathways to behaviour and influences on biology are immeasurably more complex.'

The study was published in the journal PLOS Biology.