By Kay Quinn, KSDK-TV, December 11, 2007

They can be some of the most unsettling stories we cover: young, healthy, seemingly fit people who die suddenly before or during exercise.

Hypertrophic cardiomyopathy, or HCM, is one of the most common causes of these sudden deaths, and there are symptoms related to the condition that may mean you should see a doctor.

HCM causes a thickening of the walls of the heart. It''s the most common cause of sudden death in people under 25 who exercise.

HCM was found to be the cause of death of 16-year-old Adam Litteken, a high school hockey player in St. Charles County. Litteken collapsed on the ice while warming up with his team Oct. 2.

Lisa Risenhoover, a 34-year-old wife and mother of two, who also has HCM. She was diagnosed during her first pregnancy 11 years ago at age 22.

"I went numb," said Risenhoover.

Risenhoover had symptoms before the diagnosis. She''d feel faint and dizzy after standing from a squatting position. Initially she chalked them up to pregnancy.

"HCM means that the heart functions normally, but the walls are thickened," said Dr. Keith Mankowitz, a cardiologist at Barnes-Jewish Hospital who specializes in treating patients with HCM.

He said screening all young people for heart problems can be like looking for a needle in a haystack.

But he does want people to be aware of the warning signs that can precede sudden death: palpitations of the heart, shortness of breath, fainting, and sometimes chest pain or pressure.

Any young person with those symptoms should see a cardiologist.

"(HCM is) the only condition in cardiology where we tell people not to exert themselves and we have to prevent them from participating in competitive sports," said Mankowitz. "By doing that we can prevent sudden death and there are various medications we can recommend."

More than 100 gene abnormalities have been found to trigger it. It can be passed along in families or develop from a spontaneous gene mutation.

Some patients may need surgery.

Risenhoover''s disease is managed with medication and avoiding stress and physical exertion. She feels if it weren''t for her son Brenden, she may not be here today.

"That pregnancy was the scariest day, but it turned out to be the biggest blessing of my life," said Risenhoover.

"It''s like I''m here for a reason. I''m really lucky to be here and I''m enjoying my life the best that I can."