Prenatal exposure to smoke and alcohol may increase the risk of children developing conduct problems in adolescence researchers said. Conduct disorder (CD) is a mental disorder where children demonstrate aggressive behaviour that causes or threatens harm to other people or animals such as bullying or intimidating others often initiating physical fights or being physically cruel to animals. The findings led by researchers from the King's College London showed that exposure to smoke and alcohol especially during foetal development may lead to some epigenetic changes -- chemical modifications of DNA that turns our genes on or off -- particularly in genes