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Epigenetics: Twins show differences at birth

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From “Differences Between Human Twins at Birth Highlight Importance of Intrauterine Environment” (Science Daily, July 15, 2012), we learn,

Your genes determine much about you, but environment can have a strong influence on your genes even before birth, with consequences that can last a lifetime. In a study published online in Genome Research, researchers have for the first time shown that the environment experienced in the womb defines the newborn epigenetic profile, the chemical modifications to DNA we are born with, that could have implications for disease risk later in life.

In this report, an international team of researchers has for the first time analyzed genome-scale DNA methylation profiles of umbilical cord tissue, cord blood, and placenta of newborn identical and fraternal twin pairs to estimate how genes, the shared environment that their mother provides and the potentially different intrauterine environments experienced by each twin contribute to the epigenome. The group found that even in identical twins, there are widespread differences in the epigenetic profile of twins at birth.

But then what about all those politically correct twin studies that claim to show that whether you are gay or religious or … yeah, like we thought.

The worst thing about being a taxpayer is that there is no one to complain to or ask for your money back. The best thing is, we can – so far, legally – just ignore them.

Apart from the issue of "they wuz wrong", the deeper and more interesting question is why, even at birth, the profiles are so different, and what accounts for it. As the medical father of twins who are "identical" but have never been "the same" I've often wondered about environmental differences. There are bound to be some - minor differences in placental blood flow, position in utero and so on. But these seem only small beer in pregnancy, given that the twins have the same exposure to food, drugs, sounds, hormones etc etc. Around the time of birth, there can be significant different experiences of labour - in our case the first experienced ruptured membranes and so had a few hours start in lung maturation - but both were delivered surgically. And that doesn't explain recognisably different details of facial features and so on. And biologically, why would nature allow accidental details of birth experience to dictate widespread differences for life? The bottom line seems to be that part of the creative "design" of twins (and by implication of all of us) is executed apart from genetics and with scant regard to environment. Psalm 139, taken literally, comes to mind. It's not just the fact that there are profound epigenetic differences, but why and how. Jon Garvey

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