Her father had colon cancer, and her grandmother died from it -- at just 45. So Gretchen got screened at 38 - and it's a good thing she did.
"What did your first colonoscopy find?' CBS News anchor Katie Couric asked her.
"I had a 17-millimeter polyp that was cancerous," Gretchen said. "Thirty-eight just seemed so young."
But despite the family history, Gretchen couldn't get a colonoscopy on her brother John's "to-do" list.
"Every time she asked me, I said 'yea yea, I'll get around to it one of these days,'" John said. "Anything you don't want to do is easy to put off."
But there was a new sense of urgency when Gretchen tested positive for a specific type of colon cancer that's hereditary. It's called Lynch Syndrome.
"Having the gene, you're more at risk, more quickly," Gretchen said.
Lynch Syndrome is caused by a genetic defect. If you have it, your chances of getting colon cancer go up -- to almost 80 percent. Lynch Syndrome also causes the cancer to strike earlier - lowering the average age for diagnosis from 65 down to 45.
It's just one of some 1,300 diseases and disorders that can now be predicted with genetic testing. And for families like Gretchen's, this brave new world is a mixed blessing.
"Some of us have this curiosity to know everything we possibly can. And other people are not so interested in information that might have negative consequences," Dr. Francis Collins said.
And there are other concerns associated with genetic testing. Gretchen and John have two other siblings who declined to be part of this interview, fearing their insurance companies would hold their DNA against them. But Gretchen thinks this critical information is cost-effective.
"If you get a genetic test that shows you're at risk for things, you can prevent the cancer. And I think, what more could you ask for? The insurance won't get the bills for cancer treatment, because the cancer won't develop," Gretchen said.
One month ago, John gave in and decided to be tested for the gene. A simple blood test determines if he's a carrier.
"It's not nerve racking, because now there's a sense of relief that I might not have the gene. Whereas, I felt I always did have the gene," John said after getting the blood test.
Last week, John's results came in. They showed that he does have the gene.
Though it's not guaranteed he'll get colon cancer, John knows his odds just increased significantly.
"Genetic testing clarifies risk. And knowing your risk allows you to take steps that could save your life," said counselor Anna Leininger.
The good news is colon cancer is 90 percent curable, if found early. So john should now have a colonoscopy every year. His three children will need annual screenings too, starting in their twenties - unless a genetic test proves they're negative.
Luckily, Gretchen's colon cancer was treatable - but she's not taking any chances. Yesterday, knowing that Lynch Syndrome puts her at risk for other kinds of cancers, like endometrial and ovarian, she had a complete hysterectomy.
"In some ways, do you feel as if you've opened up Pandora's box? Do you ever say 'what next?'?" Couric asked her.
"Yes, I feel like, 'oh boy, this is really a lot.' There are days it's very hard," Gretchen said. "But I look at my three kids, and I think, 'wouldn't have grandmother have given anything to have this opportunity, to be screened for all these things once a year instead of the alternative?' So that kind of keeps me going."
Meanwhile, in Washington, there's a bill awaiting President Bush's signature that would. It would allow you to have genetic testing without fear of losing your job or your health insurance.