Twins shed light on antisocial behaviour

Antisocial behaviour in children is strongly influenced by genetic factors - but only when accompanied by psychopathic tendencies, say UK scientists. The researchers, based at the Institute of Psychiatry at King's College in London, studied twins to investigate the role of genes and other factors in behaviour. Their findings, published in the Journal of Child Psychology and Psychiatry, show that antisocial behaviour with no accompanying signs of psychopathy is largely the result of non-genetic factors, such as upbringing.

The team studied 3687 pairs of seven-year-old twins, and asked teachers to rate their level of antisocial behaviour and any psychopathic tendencies, such as lack of empathy or remorse. All those in the top ten per cent for antisocial behaviour were split into two groups: those with or without psychopathic tendencies. The results showed that when present together, antisocial behaviour and signs of psychopathy had a heritability of 81 per cent, whereas antisocial behaviour alone was just 30 per cent heritable. Lead author Essi Viding said that the research has important implications. 'The discovery that psychopathic tendencies are strongly heritable suggests we need to get help for these youngsters early on', adding that 'any behaviour is influenced by multiple genes and an unlucky combination of genes may increase vulnerability to a disorder'.

Scientists have studied twins for many years, in order to measure the influence of genes and environment on a wide range of traits. They compare identical twins, who have identical genes and similar backgrounds, with non-identical twins - who also share similar backgrounds, but are no more genetically alike than ordinary siblings. In this way, researchers can estimate how much of the variation seen for a particular characteristic is accounted for by genes - a measure of heritability. A trait that is completely controlled by genes, for example eye colour, has a heritability of 100 per cent. At the other extreme, a characteristic that has nothing to do with genes, such as a scar, will have a heritability of zero.

Viding stressed that just because certain types of behaviour are strongly heritable, it did not mean that nothing could be done for children born with a high genetic risk. 'Children are open to protective environmental influences early in life and these influences can buffer the effects of genetic vulnerability', he explained. An earlier study carried out by the group found that children were more likely to be aggressive if they inherited a particular version of a gene called MAOA (monoamine oxidase A). The MAOA gene makes a protein called monoamine oxidase A, which helps control levels of brain chemicals such as serotonin. However, a genetic predisposition to antisocial behaviour appeared to be heavily influenced by upbringing: children who inherited the MAOA variant behaved normally if they were parented well.