Handedness in twins according to zygosity and chorion type: a preliminary report.

In the course of the East Flanders Prospective Twin Survey (EFPTS), handedness was assessed as part of a genealogical study (Meulemans et al., 1995) in 1616 twins (808 twin pairs) aged 6 to 28. Our findings are that, in this large population-based study with known placentation and zygosity, the often observed higher frequency of left-handedness in twins is confirmed, that it appears to be independent of zygosity and chorion type, and that the belief that discordant handedness in monozygotic twins represents mirror-imaging is mythical.