'Protective Gene' May Help Some Live to 100

Neddine Parker is up by 7 in the morning. After her morning exercises and chores, she drives to the local hospital, where she volunteers once a week.

What makes Parker's routine so extraordinary is that she is 104 years old.

"I don't know why I'm still here," she said.

Dr. Thomas Perls of the Boston University Medical Center is trying to figure that out. As the director of the New England Centenarian Study, he studies these "super humans," those age 100 years and older.

"It's like winning the lottery," he said. "You've got to get to the right numbers and the right combination."

Researchers believe about 30 percent of aging is genetic. For those who get to extreme old ages, family history may play an even more important role.

Reuben Landau's mother lived to 100, and three of his siblings into their 90s. Landau is nearly 102, and he still practices law a few hours every day.

"It's stimulating," he said. "Otherwise it's a long day."

Both Landau and Parker are remarkably healthy. They take few medications and have no major illnesses.

Lacking Gene Linked to Illness

Perls has found that many centenarians lack a type of gene -- E4 -- that is associated with an increased risk of heart disease and Alzheimer's. One study found the gene is in 29 percent of young men, but only 15 percent of centenarians.

Perls also believes they may have a "protective gene," one that helps them survive what might kill others.

Parker, for example, smoked until she was 100 and had a stroke at 89.

"Slight stroke," she said. "But I wasn't even aware of it."

Researchers are also studying the children of centenarians.

"Well certainly to have my mother's genes would be the way to go," said Gerry Jackson Kerdok, a daughter of a centenarian.

Compared to others their same age, these offspring's rate of heart disease, diabetes, stroke and high blood pressure is 60 percent lower.

But living into your 100s isn't just genetics. Aging successfully has much to do with environment and behavior.

Landau watches what he eats and exercises his body and mind every day. He's convinced it's why he's still in good health.

"People still have to do the right things to still get to very old age," said Perls.

So it's not just the cards you're dealt, but how you play the hand.

ABC News' Lisa Stark filed this report for "World News Tonight."