Although many physically maltreated children develop behaviour problems, some maltreated children are resilient and avoid them. A new study suggests that a 'polymorphism' in a particular gene may be responsible for this difference.

A polymorphism is a condition in which a chromosome or genetic character occurs in more than one form, resulting in the co-existence of more than one structural type of gene in the same population.

This study, conducted at Yale University and the Institute of Psychiatry, King's College in London, evaluated the role of a genetic variant in the monoamine oxidase A (MAOA) gene in predicting which children are vulnerable or resilient to the effects of abuse.

2 methods were used. First, data analyses were carried out on 975 Caucasian boys in the Environmental Risk (E-Risk) Longitudinal Study. Mothers were interviewed about boys' lifetime experience of physical abuse and exposure to domestic violence.

Mothers and teachers reported on the boys' antisocial behaviour, attention-deficit hyperactivity disorder (ADHD) symptoms, and emotional difficulties.

DNA samples were obtained from the boys, and genotyped for a polymorphism in the MAOA gene.

Second, a meta-analysis was undertaken of 7 studies involving the MAOA-by-maltreatment gene-environment interaction.

It was found that in the E-Risk sample, maltreated boys carrying the low-activity MAOA polymorphism had significantly higher levels of mental health problems than maltreated boys carrying the high-activity polymorphism.

Further analysis revealed that this gene-environment interaction was significant in predicting ADHD symptoms, but not antisocial behaviour or emotional difficulties.

The researchers conclude that the evidence so far indicates that one reason why some maltreated children develop behaviour problems while others do not may have to do with differences in underlying biochemistry and neurological functioning associated with a polymorphism in the MAOA gene.

Royal College of Psychiatrists