Genes influencing response to life experiences identified in largest twin study

The largest ever international twin study has uncovered genetic markers that could explain why people respond differently to similar environmental pressures.

The study specifically looked at the development of psychiatric and neurodevelopmental conditions, and the severity of symptoms experienced. These included ADHD and autism, anxiety, depression, and psychotic experiences.

'Differences in individuals' sensitivity to life experiences can explain why the same negative or positive experiences may have varying effects on people's mental health, depending on their genetic make-up,' said Dr Elham Assary from King's College London, first author of the study published in Nature Human Behaviour.

Twin studies are a way of understanding the relative contribution of genes and external factors to various traits and outcomes. Because identical (monozygotic) twins inherit the same genome, differences that emerge during their lives can be attributed to environmental factors.

In this case, if the twins' genome contains variants that make them more sensitive to environmental circumstances such as traumatic events, more differences should emerge between the pair than between other sets of twins less sensitive to these conditions.

Researchers from 26 universities around the world conducted genome-wide association study (GWAS) on the phenotypic differences between 10,896 pairs of twins at multiple ages.

The results found links between genes encoding growth factors and autism, and between depression and genes linked to stress reactivity.

A link between anxiety symptoms and a gene encoding a protein that regulates appetite allowed the researchers to suggest a mechanism for the connection. Noting the similarities between the 'unpleasant physical sensations' of low blood sugar – such as rapid heartbeat – and nervousness and anxiety, they proposed that variants in this gene could impact people's sensitivity to changing insulin levels, manifesting as the physical sensations associated with worry.

However, the authors noted that their findings do not prove that these links constitute causation.

'These findings confirm that genes influence psychiatric and neurodevelopmental traits partly through affecting how people respond to the world around them,' said joint senior author Thalia Eley, professor of developmental behavioural genetics at King's College London. 'Some people are more sensitive to their circumstances, and this can be positive in good circumstances but can make life more challenging than for others in stressful circumstances.'

The limitations highlighted within the paper included that all twins in the study were of European descent, which the researchers mentioned they would like to expand in future.