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Why do mood and behavioural disorders seem to run in families?

Mother, father and child

A large-scale Trust-funded study is helping to show how parents' mental states are passed on to the next generation, and to unravel the genetic and life events that cause mood and behavioural disorders in children.  

The Avon Longitudinal Study of Parents and Children (ALSPAC) project, supported by the Wellcome Trust and MRC since 2001, recruited around 14 000 expectant mothers in 1991. It has followed the development of their offspring (now aged 18-19) ever since, collecting biological samples and information about health and lifestyle.

Researchers at universities across the UK mining the data discovered that children whose mothers experienced high levels of anxiety during pregnancy are more likely to develop asthma. This is likely to be an example of an epigenetic effect - the stressful environment in the womb causing alterations to the way genes are expressed in the fetus.

ALSPAC data also revealed that bullied children are up to four times more likely to develop psychotic-like symptoms such as hallucinations, delusions or paranoia - in adolescence, for example. And boys whose fathers were depressed both before and after they were born have an increased risk of conduct problems in boys. The risk grows in proportion to the duration of the father's depression. 

A father's depression seems to have a specific and lasting effect on his child's early development. However, it is not clear is whether this is because the father's 'depressed' genes are passed down to the child, or whether the baby's emotional development is affected by the father's mood (an environmental effect). There may also be an epigenetic effect before birth, if the impact of the father's depression on the mother affects the fetus in her womb.  

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