Genetic and environmental architecture of synesthesia and its association with the autism spectrum - A twin study

Abstract Synesthesia is a sensory phenomenon where external stimuli, such as music or letters, lead to additional sensations of, e.g., specific colors. Synesthesia aggregates in families and is more common in people on the autism spectrum compared to the general population. We used classical twin design in order to assess the heritability of individual differences in synesthesia and the genetic and environmental contributions to their association with autistic traits. Individual differences in synesthesia were estimated to be heritable and influenced by environmental factors not shared between twins. The autistic trait-domain of repetitive behaviors, restricted interests and attention to detail appeared to be driving the association between total autistic traits and synesthesia. The associations between individual differences in synesthesia and autistic traits was estimated to be mainly (>70%) under genetic influence. In sum, synesthesia appears to be heritable and genetically linked to primarily non-social autistic trait domains.