However, consonant with the findings of previous single-pair case studies, our large sample size verifies
that synesthesia is not completely conferred by genetics; if it were, monozygotic twins should have 100%
concordance. These findings implicate a genetic mechanism of CSS that may work differently than previously
thought: collectively, our data suggest that synesthesia is a heritable condition with incomplete
penetrance that is substantially influenced by epigenetic and environmental factors.