The O'Brien's have hours of memories, from the top of the world.
There's home video of Michael, with kid brother Chris, at Everest base camp.
The experienced mountaineers attempted their first grueling trek up Mt. Everest's 29,028 feet last month.
"Every new vista that we climbed up to was just a beautiful creation," remembers Chris.
But it wasn't just for thrills. It was to raise awareness and money to fight Huntington's disease, a rare illness that killed their mother and a sister. The genetic disorder slowly destroys the brain. There is no treatment and no cure.
Most families, like the O'Brien's, keep it hidden.
"That's what makes it very difficult for fundraising for research," says Dr. Nancy Wexler with the Hereditary Disease Foundation. "People don't want to admit it's in the family."
Experts say only about 35,000 Americans suffer with Huntington's disease, an illness that usually first strikes people in their 30s and 40s, when some already may have passed it on to their kids.
Most of the O'Brien's never have been tested for Huntington's. Like Michael, they prefer not to know.
"He didn't want to take a chance that life was going to be short, so he lived now," says Michael's girlfriend Rebecca.
As he was on Everest, about midway through the trek, the weather turned bad.
"I was able to rappel down to Mike's side," recalls Chris.
Michael had fallen 40 feet down into a crevasse, breaking a leg and several ribs.
"It was desperate," says Chris. "His breathing became more and more labored. And, you know, he was apologizing, sorry. I said, 'for what?' We talked for a good 45 minutes before he stopped breathing."
"Mike's death is almost merciful, because it would have killed him to watch his siblings get sick," says Rebecca.
Thursday, the O'Brien's hometown of Oswego, N.Y. paid its respects.
As word of what happened has spread, more than one million people have visited their Web site: OBriensEverest.com.
Chris, training to be a doctor, hopes to make finding a cure for Huntington's disease part of his brother's legacy.
"He just wanted to do anything he could to bring awareness to the world about this disease," says Chris.
He did that, even without reaching the top of the world.