Mutated DNA may explain some obesity

Marisa O’Neil

Any woman who’s ever blamed her mother for her own ample hips may

take heart in a new study. But they’ll likely have to look further

back than their own mother.

A team of researchers at UC Irvine published a report in the Jan.

9 issue of “Science” linking obesity and some age-related conditions

to maternally-inherited genes in mitochondrial DNA. Certain gene

mutations in early humans, who migrated north from warmer climates,

helped them adapt to the cold and burn calories more efficiently,

according to the report by the school’s Center for Molecular and

Mitochondrial Medicine and Genetics.

“In the Arctic what was going to kill [early humans] 10,000 years

ago was the extreme cold in the middle of winter,” said Douglas

Wallace, director of the center and co-author of the study. “Those

who survived, their [genetic] blueprints got changed and the amount

of energy in their bodies that goes to make heat increased.”

The mutations would have helped those people survive as they moved

from Africa to the higher latitudes and colder temperatures of Europe

and Asia while other humans died off. Descendants of people with the

mutated gene may be less prone to certain health problems because of

the way their bodies burn calories, Wallace said.

Mitochondria, located outside a human cell’s nucleus, burn

calories in our diets. That energy creates heat, which regulates body

temperature, and synthesizes adenosine triphosphate, a chemical that

allows people to think, move and make and repair cells and tissues.

Wallace likened mitochondria to a power plant and the

mitochondrial DNA to its blueprints, which determine how many

calories go to heating the body and how many go to performing tasks.

“If 90% of the energy from burning calories goes to making

[adenosine triphosphate], that efficient design is encoded in the

blueprint,” Wallace explained. “But if only 70% of the calories go to

that and the rest go to heating, that’s also in the blueprints.

People who live in the tropics, where it’s hot all the time, don’t

want a lot of waste heat. They are more efficient at making heat

work.”

If an Inuit Eskimo and native Kenyan ran a 220 dash, he said as an

example, the Kenyan would win with little effort because he would not

have the mutated gene and his body more efficiently sends energy to

his muscles.

On the other hand, the Eskimo who has the gene that has allowed

him to adapt to extreme cold, would win the same race in the Arctic

and the Kenyan would freeze to death.

Because the body produces oxygen radicals -- also known as free

radicals -- when mitochondria burn calories, how a person’s body uses

energy can affect their health. Someone with the mutated gene, he

said, would be more adapted to consume a higher fat diet without

producing excessive free radicals, which can build up to kill cells,

damage organs and age the body.

“People with cold-adapted genes are burning very hot,” Wallace

said. “They are generating a lot of excess heat and give off little

oxygen radicals. A person from the tropics who eats McDonalds

hamburgers is burning an efficient system and doesn’t need all those

calories.”

Europeans and Americans, he said, are a mixed bag of those with

the mutation, which is only passed on by the mother, and those

without. Understanding more about other genes will further explain

why higher fat and calorie diets affect some people more than others

and may help prevent age-related illnesses.