first of all, thank you for the reaction to my post and: welcome to my blog!

Obviously, I bring my argument quite strongly, to emphasize the importance of this finding. But, I chose my words carefully: I explicitly wrote that I do not want to throw all findings based on this assumption “out of the window’, but I do argue that re-evaluation is called for.

The argument you give about the difference between genotype and phenotype actually is not that strong. Rather, I think it implicitly emphasized the importance of my interpretation. You write that for long we now that phenotype of monozygotic twins can differ. This is true, but until now, the differences in phenotype have not been attributed to genetic differences. Thus, they were attributed to environmental influences (i.e. personal choices made, social environment, etc.), but this cannot be done any longer from now on. At least not as an automatic assumption, for we now know that monozygotic twins can differ both genetically and phenotypically.

You really make this way more dramatic than it is. Based on phenotype it is easy to deduce that their must be some genetic differences between identical twins (e.g. Frank and Ronald de Boer look different). The paper just confirms that a long suspected cause for this difference is indeed there. Still, the difference is small and in most cases probably insignificant compared to environmental factors.