As a kid, Brandon Colby couldn’t play tennis without his hand breaking out in blisters just from gripping the racket. Today, a two-block walk on a warm spring day can give him blistered feet.

Colby learned when he was young that his mystifying condition was the result of a rare genetic mutation that made his skin highly sensitive to heat and friction. He became fascinated by genetics, figuring that even if he couldn’t discover a cure for his condition, he might be able to help others. So he became a doctor and an entrepreneur.

He now has something to show for his years of study, research and development. Colby’s West L.A. company, Existence Genetics, is rolling out a genetic test to predict the risk for developing diseases such as cancer and conditions such as cardiac arrhythmia. With early detection, doctors and patients can take measures to reduce risk.

“I always had to sit on the sidelines as a child, but now I want to be at the forefront of the genetic revolution,” said the 33-year-old Colby, whose company is one of a growing number of firms riding the wave of increased interest in a genetic approach to health care. “My genes were causing me a lot of pain and suffering, and I wanted be empowered to take back control and enable other people to do that, too.”

Among Colby’s innovations is a saliva test chip – slightly larger than a stick of gum – that can evaluate DNA at a lower cost than some other methods. He is using it in his practice and has begun making arrangements for other doctors also to use it.

The findings are run through a database to identify the genetic markers for higher risk for melanoma, sudden death from a heart arrhythmia, and other conditions and diseases.

Existence Genetics’ test is in the midpoint of two extremes on the DNA testing scene. On the high end is full-genome sequencing that costs thousands of dollars and is available only at academic research hospitals. On the low end is a recent spate of Internet companies offering cheaper over-the-counter tests that have begun attracting the scrutiny of regulators.

The cost for Colby’s test should run between $400 for a specialized panel for certain conditions to about $900 for a more comprehensive panel that screens for more than 700 diseases and traits.

He also offers the higher-end test as the grand prize for a Facebook page contest. But he insists that testing should be done under a doctor’s supervision and interpretation.

Colby is promoting the test through his blog and wants to sell the test through doctors. The program he offers doctors allows them to customize test panels, protect privacy and co-brand the reports given to patients.

Customization means that family practitioners could offer a comprehensive test that could pick up increased risks for cancer and heart attack, or sports medicine specialists could look for markers that could help explain why an athlete excels at weight lifting but struggles to finish a marathon or other performance issues.

“Our expertise is in turning all those letters and numbers related to a person’s genome into something intelligible that they can take action on,” Colby said. “I want people to be able to say, ‘OK, so I’m susceptible for developing colon cancer – here’s what I can do to lower my risk.’ ”

Colby created his own major in genetics through the University of Michigan Honors Program in 1996, and later earned a medical degree from the Mount Sinai School of Medicine in New York. After time in research and medical practice, he decided to launch his own company. The business plan for Existence Genetics took shape five years ago while Colby was earning his M.B.A. at Stanford University’s Graduate School of Business.

He still suffers from epidermolysis bullosa, an inherited connective tissue disease that causes blisters to form when a person’s skin temperature rises above a certain level due to simple friction. Research for a cure is continuing.

Sheldon Collins, a Brentwood medical device sales rep who got tested after reading Colby’s 2010 book “Outsmart Your Genes,” said the results confirmed that he had inherited the same proclivity for heart disease as several of his family members.

“You don’t think of preventative health in your 20s and 30s, but I’m coming up on 40 and preparing to get married and start a family. So, yeah, I’m thinking a lot more about what I can do to live long and healthy,” said Collins, who became more conscientious about his diet and exercise regime.

He also learned, to his relief, that he’s at less risk for melanoma and other cancers.

Dr. Sharon Plon, director of the Baylor College of Medicine’s Cancer Genetic Clinic in Houston, said Existence Genetics will face plenty of competition from government agencies, academic institutions and for-profit companies that are investing millions of dollars to make genetic testing an effective diagnostic tool.

Plon sees genetic testing as a valuable component of doctors’ work with patients.

“The more you can integrate the information and provide an understandable report, the better,” she said.

Dr. John LaLonde, part of a family practice group in Costa Mesa, expects to offer the test as an option for patients willing to pay the full cost, since most such tests are not yet covered by insurance.

“As a primary care doctor, I’m attracted by the potential for learning things about a patient that may not come up when I’m getting their medical history,” LaLonde said. “Maybe it will help me twist people’s arms about making changes in their lives.”