Before revision: Due to the prevalence of synesthesia among the first-degree relatives of synesthetes, there is strong evidence that synesthesia has a genetic basis, however the monozygotic twins case studies indicate there is an epigenetic component.
After revision: Due to the prevalence of synesthesia among the first-degree relatives of synesthetes, there is strong evidence that synesthesia might have a genetic basis, however the monozygotic twins case studies indicate there is an epigenetic component.