Largest twin study explores whether the environment affects people differently depending on their genes

Published today in Nature Human Behaviour, the study examined how individuals’ varying sensitivity to environmental factors can influence levels of ADHD symptoms, autistic traits, anxiety and depression symptoms, psychotic experiences and neuroticism.  

Led by researchers at the Institute of Psychiatry, Psychology and Neuroscience (IoPPN) at King’s College London, colleagues from University College London, Queen Mary University of London, and 23 universities around the world combined data from up to 21,792 identical twins (10,896 pairs) from 11 studies to discover genetic variants linked with environmental sensitivity. This is the largest genome wide association study (GWAS) of identical twins to date. 

Researchers identified several genetic factors that were linked with differences in environmental sensitivity within identical twin pairs. The interaction between these genetic factors and environmental exposures could explain differences in susceptibility to psychiatric and neurodevelopmental conditions. 

Professor Patricia Munroe, Professor of Molecular Medicine at Queen Mary University of London and joint senior author of the study, said: “The results from this study provide an important step forward in disentangling gene-environment interactions for psychiatric traits and provide a framework for similar investigations in other traits.” 

Both genes and life experiences shape a person’s characteristics, including the expression of conditions such as depression, anxiety, ADHD and autism. The interaction between genetics and environmental exposures are thought to contribute to diversity in a wide range of traits within all species. But, identifying the genes that are involved in this pathway has proved challenging, especially for complex psychological traits. 

Identical (monozygotic) twins are almost 100 per cent genetically identical, meaning that any differences in their characteristics are likely to be due to the environments they each experience. If a monozygotic twin pair carries genes that make them more sensitive to the effects of the range of unique environments they each experience (for example, relationships or traumatic events), they will be more dissimilar to their co-twin, compared to another pair that is less sensitive to these experiences. Using this information, it is possible to scan the genome to identify the genes that impact variations in environmental sensitivity. 

Among the genetically identical twins, the researchers discovered genes that explained variations in autistic traits, anxiety, depression, psychotic-like experiences and neuroticism, reflecting heightened environmental sensitivity. 

They found that genes linked with growth factors – biological molecules which play important roles in neurodevelopment, immune function and the central nervous system – were associated with variation in autistic traits. Genes related to reactivity to stress were linked to variation in depression symptoms. Genes involved in regulating catecholamines – a group of hormones involved in response to stress – were linked to variation in psychotic-like experiences.  

The study received funding from Wellcome and used twin datasets from around the world: the Danish Twin Registry, Finnish Twin Cohort, Murcia Twin Registry, Netherlands Twin Registry, Older Australian Twins Study, Swedish Twin Registry, Twins Early Development Study, TwinsUK and QIMR Berghofer twin studies.