(CBS) -- There are now more than a thousand genetic tests, for everything from baldness to breast cancer, and the list is growing. Question is, do you really want to know what might eventually kill you?
That knowledge, some scientists say, could ruin the life you have now.
For instance, Nobel Prize-winning scientist James Watson - one of the first people to map their entire genetic makeup - is said to have asked NOT to be told if he was at higher risk for Alzheimer's.
"If I tell you, particularly incorrectly, that you have an increased risk of getting a terrible disease, that could weigh on your mind, that could make you anxious," said Dr. Robert C. Green of Boston's Brigham and Women's Hospital. "That could be the filter through which you see the rest of your life as you wait for that disease to hit you. It could really mess you up."
"Every ache and pain," Smith suggested, could be interpreted as "the beginning of the end."
"That's right. If you ever worried you were at risk for Alzheimer's disease, then every time you can't find your car in the parking lot, you think the disease has started."
Dr. Green is a Harvard geneticist who has been pondering this issue for years. He led a study of people who wanted to know if they were at a higher genetic risk for Alzheimer's. It was thought that people who got bad news would, for lack of a better medical term, freak out.
But Green and his team found that there was "no significant difference" between how people handled good news and possibly the worst news of their lives. People who ask for the information usually can handle the information, good or bad, said Green.
In fact, most people think they can handle it: According to a CBS News poll, 58 percent of Americans said they would want to know if they carried a gene for an incurable disease.
Dr. William Harbour, of Miami's Bascom Palmer Eye Institute, is a pioneer in treating ocular melanoma - eye cancer. He's also developed a new genetic test that divides patients into two classes of survivability: Class I or Class II.
Very simply, Class I cancer cells act like normal cells and can be killed. In Class II, the cells have mutated and have begun to spread throughout the body. There is no cure for Class II.
As far as accuracy goes, compared to other genetic tests out there, where does Dr. Harbour's stand? He replied, "I'm told by my colleagues in other fields of oncology that this is perhaps the most accurate prognostic test of any cancer. Certainly among the most accurate of any cancer."
Now, when his patients inevitably ask if the disease will kill them, Harbour has a more accurate answer.
Sunni Ziroff already knew she had ocular cancer when she first saw Dr. Harbour. He gave her the option of peering into her future.
"And so what did that mean to you, class I versus class II?" Smith asked.
"Whether you live or die, quite honestly," Ziroff said. "I mean, you don't know. It scares you and sets you straight up where you want to know. To me, I did."
"But if there's no proven treatment, there's no cure, why would you want to know?"
"'Cause I have a bucket list," Ziroff said.
As a veteran ER doctor, Scott Gaines is used to patients asking him what their chances were. But two and a half years ago he was diagnosed with eye cancer as well, and found himself in Dr. Harbour's clinic.
"And I had to ask him, I said, 'Well, can you tell by looking? You know, come on, give me some odds. What do you think? You've seen enough of these,'" Gaines recalled. "And he didn't answer it the way I wanted. It was 50/50. And he wouldn't go past 50/50 - Class I, Class II, and did I want to have the test? And, well, of course, I want to know."
Dr. Harbour said even if a patient can't be cured, "people generally want to have more information. They may modify the way they live their life."
Dr. Harbour learned that personally, when his own father was diagnosed with melanoma. "I knew that the doctors couldn't cure him, but I knew that he only had a certain amount of time to live, and it dramatically altered how I interacted with my father and how our family interacted with each other. And by the time he died we all felt that we had come to a good place."
"These are precious moments<" said Smith.
"Correct," he said.
But Dr. Evangelos Gragoudas of the Masschusetts Eye and Ear Infirmary says knowing your fate does no good, if nothing can be done. "Personally, I don't, but I completely understand somebody who wants to know that," he said.
Dr. Gragoudas tells his patients about the ocular melanoma test, but he won't recommend it.
If asked his opinion, "I would say that I wouldn't do it for myself, or for any member of my family because if I found that this tumor is highly malignant, the so-called Class II category, I have nothing to offer to the patient."
And what you know can hurt you in other ways: People who are at higher risk for disease - and know it - may have problems with insurance, though that discrimination is illegal.
Still, for many there is no such thing as ignorant bliss.
Nicola Powers died at age 45 from Huntington's, a rare, degenerative neurological disease for which there is no treatment or cure. Her daughter Kristen grew up knowing there was a 50-50 chance she'd die the same way.
"I think one of the big questions you have to ask yourself is, is the burden of knowing greater than the burden of not knowing?" Kristen Powers said.
For the 18-year-old the burden of not knowing was too much. She got tested last May - and braced herself for the results.
"I think it is very hard to face a moment where you're going to learn for sure that your future is truncated," said Dr. Green. "That you're going to get this terrible disease, often the same disease you've watched your parent decline with. So I think people make their own personal decision, and I think either decision is fine. But they're faced with this very, very dramatic moment."
Those moments could soon be happening more often, for more people: Americans spent $5 billion on genetic testing in 2010, and that number is expected to quintuple in the next decade.
"Maybe even ten years from now, certainly 20 years from now, it would be unthinkable not to have your genome as a resource for your own health," said Dr. Green.
"And you think most people will take advantage of that?" Smith asked.
"Absolutely. I think it will be as common as getting your blood pressure taken."
The people we profiled in this story all decided genetic testing was worth a try. They wanted to know, and they gave us permission to share their results.
Kristen Powers - now a freshman at Stanford - tested negative for Huntington's. Neither she nor her children will get the disease. She's making a documentary about her experience.
Sunni Ziroff's cancer is Class I, so there's a good chance she's cancer-free. Her bucket list will have to wait.
Dr. Scott Gaines' cancer is Class II. His cancer has spread, and now every day is precious as never before.
"I like to savor moments, savor things, smell, teach my boys to smell, remember this. Get all your senses into it," said Dr. Gaines. "Would I have done that if I was a Class I? I don't know."
At this point, he's already outlived his prognosis. "I feel fine. I shouldn't feel fine, Tracy, [but] I do," he said. Why is that? I think most people'll tell you I got a good attitude. You know, is it prayer? Is it what? I don't know. Will tomorrow it decide to act like a Class II? I don't know. I'm not waitin'. Am I still getting scans frequently? Oh, you bet I am."
And no genetic test can replace another powerful force in medicine: Hope.
"How 'bout five, ten years from now? Where do you think you'll be?" Smith asked.
"Well, I hope I'll be a granddad then," Dr. Gaines replied.