Study shows individual genome changes over a lifetime

Washington, June 25 : Certain types of chemical, or epigenetic marks on an individual's DNA sequence change during his or her lifetime and the amount of change is similar among family members, according to a new study by Johns Hopkins researchers.

The researchers say that their findings may explain why people become more susceptible to disease as they age and why the health of one's genes is similar among families.

"We're beginning to see that epigenetics stands at the center of modern medicine because epigenetic changes, unlike DNA sequence which is the same in every cell, can occur as a result of dietary and other environmental exposure," says Andrew P. Feinberg, M.D., M.P.H, a professor of molecular biology and genetics and director of the Epigenetics Center at the Johns Hopkins School of Medicine.

"Epigenetics might very well play a role in diseases like diabetes, autism and cancer."

If epigenetics does contribute to such diseases through interaction with environment or aging, says Feinberg, a person's epigenetic marks would change over time.

So his team embarked on an international collaboration to see if that was true. They focused on methylation-one particular type of epigenetic mark, where chemical methyl groups are attached to DNA.

The researchers used DNA samples collected from people involved in the AGES Reykjavik Study (formerly the Reykjavik Heart Study). Within the study, about 600 people provided DNA samples in 1991, and again between 2002 and 2005. Of these, the research team measured the total amount of DNA methylation in each of 111 samples and compared total methylation from DNA collected in 2002 to 2005 to that person's DNA collected in 1991.

They found that in almost one-third of individuals, methylation changed over that 11-year span, but not all in the same direction. Some individuals gained total methylation in their DNA, while others lost.

"What we saw was a detectable change over time, which showed us proof of the principle that an individual's epigenetics does change with age," says M. Daniele Fallin, Ph.D., an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.

"What we still didn't know was why or how, but we thought 'maybe this, too, is something that's heritable' and could explain why certain families are more susceptible to certain diseases."

The team then measured total methylation changes in a different set of DNA samples collected from Utah residents of northern and western European descent. These DNA samples were collected over a 16-year span from 126 individuals from two- and three-generation families.

Similar to the Icelandic population, the Utah family members also showed varied methylation changes over time. But they found that family members tended to have the same kind of change-if one individual lost methylation over time, they saw similar loss in other family members.

"We still haven't concretely figured out what this means for health and disease, but as an epidemiologist, I think this is very interesting, since epigenetic changes could be an important link between environment, aging and genetic risk for disease," Fallin says.

The study appears in the June 25 issue of the Journal of the American Medical Association.

ANI