If you want to follow science over at least half a lifetime as I have, you need to be ready to discard one paradigm for another when the data clearly show the old paradigm is not the best explanation for a natural phenomenon or process. Such is the case with a new paper by Bruder et al. that demonstrates that monozygotic twins are not in fact genetically identical, at least as far as somatic tissues (non-germ line cells) go. They confirm in such twins that there is considerable gene copy number variation just as has recently been demonstrated for unrelated individuals. The authors, with caution, suggest using their methods to identify disease associated loci in discordant monozygotic twins (one twin is affected, but the other twin is not). So, I think we need to drop the identical twin moniker in favor of monozygotic to be more accurate in our speech.
Bruder et al., Phenotypically Concordant and Discordant Monozygotic Twins Display Different DNA Copy - Number - Variation Profiles, The American Journal of Human Genetics (2008), doi: 10.1016 / j.ajhg. 2007.12.011 (in press)
