Genetic and environmental contributions to the link between synaesthesia and neurodevelopmental and psychiatric features: a twin study.

Researchers studied synaesthesia (when one sense automatically triggers another, like seeing colours when hearing sounds) in twins. They found that people with synaesthesia were more likely to have traits related to autism, ADHD, anxiety, depression, and other conditions. The strongest link was with obsessive-compulsive behaviours. The study showed these connections are mainly due to shared genes rather than environmental factors, suggesting synaesthesia and these conditions may have common genetic causes.

This twin study examined the relationship between synaesthesia (a sensory phenomenon where one sense triggers another) and various neurodevelopmental and psychiatric features in 18-year-old twins. All assessed features including autism, ADHD, obsessive-compulsive disorder, anxiety, depression, psychotic-like experiences, eating disorders, and mania showed positive correlations with synaesthesia. The strongest association was with obsessive-compulsive features (r = 0.28). Classical twin modelling revealed that genetic factors explained over 50% of most associations, while shared environmental factors had negligible influence.

Non-shared environmental factors contributed variably to different associations. The findings suggest synaesthesia shares genetic pathways with multiple neurodevelopmental and psychiatric conditions rather than being specifically linked to autism.

Clinicians should be aware that synaesthesia may co-occur with various neurodevelopmental and psychiatric features, particularly obsessive-compulsive traits. The strong genetic component suggests potential shared biological pathways that could inform future research into common mechanisms underlying these conditions.

Sample size not reported, limiting assessment of study power. Relies on self-reported synaesthesia which may introduce measurement bias. Cross-sectional design prevents causal inference. Limited to 18-year-old twins, reducing generalizability across age groups.

Synaesthesia is a sensory phenomenon where specific inputs such as written letters or tastes automatically trigger additional sensations (for instance colours). The phenomenon is more common in people on the autism spectrum compared to the general population and seems also to be associated with other neurodevelopmental and psychiatric conditions and features. We assessed the associations between self-reported synaesthesia and eight psychiatric / neurodevelopment features in 18-year-old twins and estimated the genetic and environmental contributions to these associations using classical twin modelling. All of the neurodevelopmental / psychiatric features (related to autism, ADHD, obsessive-compulsive disorder, anxiety, depression, psychotic-like experiences, eating disorders, and (hypo-)mania) correlated positively with self-reported synaesthesia.

The strongest association was found with obsessive-compulsive features (r = 0.28). Genetic factors explained more than 50% of most these associations. Environmental factors that are not shared by twins (non-shared environment) influenced the associations to different degrees, while the influence of environmental factors that are shared by twins was estimated to be negligible. Rather than being specifically linked to autism, synaesthesia seems to be associated with a wider range of neurodevelopmental / psychiatric features, and especially obsessive-compulsive features.

Genetic factors play a predominant role in most of these associations, suggesting that synaesthesia might share part of its genetic causes with several neurodevelopmental / psychiatric conditions.