Even identical twins grow apart genetically -study

WASHINGTON (Reuters) – Identical twins grow apart,genetically, as the years pass, a team of European and U.S.researchers reported on Tuesday.

Their study of identical twins show the genetic code itselfdoes not change, but rather chemical changes after birth alterthe way the gene is expressed, a process known as epigenetics.

The study, which involved researchers and twins in Spain,Denmark, Britain, Sweden and the United States, can help shedlight on how environment and genes interact to produce diseaseand ordinary differences between people.

They studied 80 twins from Spain, and found significantepigenetic differences in 35 percent of them. The younger pairsof twins were identical, while the older pairs were more likelyto differ from one another.

“Most importantly, we found a direct association betweenthe remarkable epigenetic differences observed and the age ofthe monozygotic (identical) twins: the youngest pairs wereepigenetically similar, whereas the oldest pairs were clearlydistinct,” the researchers wrote in this week’s edition of theProceedings of the National Academy of Sciences.

“Our study reveals that the patterns of epigeneticmodifications in (identical) twin pairs diverge as they becomeolder.”

Identical twins occur in one out of every 250 births aroundthe world. But although their genetic codes are virtuallyidentical, there are clear differences that are obvious to morethan just their mothers.

For instance, psychiatric diseases such as schizophreniaand bipolar disease do not occur uniformly among identicaltwins. And there are often physical differences.

“There are several possible explanations for theseobservations, but one is the existence of epigeneticdifferences,” Manel Esteller of the Spanish National CancerCenter in Madrid and colleagues wrote.

This supports theories that environmental factors, such assmoking, diet and exercise, affect DNA directly, theresearchers said.

It is also possible that, just as DNA mutations occur withsimple aging, the epigenetic effects on genes also “drift” withage, the researchers said.