Chemical changes to our DNA may make us obese, a genetic study shows.

When looking for genetic causes of disease, most researchers try to find out how the genetic code of people with the disease differs from the genetic code of healthy people.

Johns Hopkins researcher Andrew Feinberg, MD, MPH, and colleagues took a different approach. They know that sometime in life, methyl chemical groups attach to some of a person's DNA. These chemical attachments can act as dimmer switches that affect how the gene works.

Some of these "epigenetic" changes are genetically determined. Others appear to happen very early in life and are pretty much permanent. Still others happen through the life span, and may or may not be permanent. Identical twins have identical DNA when they are conceived -- but as they age, the chemical attachments to their DNA grow more and more different.

Can these changes make a person more or less vulnerable to disease?

To find out, Feinberg and colleagues looked at 4.5 million DNA sites in 74 elderly Icelandic people participating in a gene study. Participants gave blood samples twice, with 11 years between measurements.

Some of the people in the study were obese. Others were not. Feinberg and colleagues found 13 changes that were much more common in the obese people. Four of these changes remained the same in the two tests 11 years apart.

The changes were in genes scattered across the human genome.

"Some of the genes we found were ... previously suspected, but not confirmed, for a link to body mass," Feinberg says in a news release. "Others were a surprise -- such as one known to be associated with foraging behavior in hungry worms."

The researchers suggest that if their findings are confirmed -- and if the changes begin in childhood and remain stable -- tests might be able to identify children at highest risk of growing up obese.

And it's not all about obesity. The same techniques, Feinberg and colleagues suggest, can be used to look for epigenetic changes linked to diseases such as autism, diabetes, asthma, and bipolar disorder -- or even life span.