It's called sickle-cell trait, and many of those who have it never know they do. That's because it rarely causes symptoms and is not even considered a medical condition or disease.
"It only very rarely leads to problems -- it's almost always benign," said Dr. James R. Eckman, an expert in sickle-cell trait and a professor of hematology and oncology at Emory University in Atlanta. "But under the extremes of human endurance, there can be problems. People need to understand this is a very unusual situation."
The Orange County medical examiner has ruled that sickle-cell trait made Plancher susceptible to the loss of blood flow, the muscle breakdown and the heartbeat irregularities that killed him during a March 18 offseason workout with the UCF football team. The examiner's office declined to comment Friday beyond a two-paragraph statement that summarized its findings.
People with the trait have one flawed gene that affects some of their hemoglobin -- the protein in red blood cells that carries oxygen to the body's tissues and organs.
The protein mostly comes in two forms: hemoglobin A and hemoglobin B. But in people with the errant gene, the body makes another form -- hemoglobin S. At most, hemoglobin S makes up about 40 percent of the protein in those with sickle-cell trait, said Dr. Paul Gordon, a hematologist and oncologist with Nemours Children's Clinic Orlando. And so it does not cause problems.
"There are more than enough normal red blood cells," Gordon said.
The real danger is sickle-cell disease, also known as sickle-cell anemia.
People with sickle-cell disease inherit two errant genes and churn out more hemoglobin S. The protein causes the red blood cells to become misshapen and sticky, so they clump together. They can clog up arteries in the body, hampering blood flow.
Complications from that include infections, strokes and pain -- excruciating pain all over the body, said Dr. Willarda V. Edwards, president and chief operating officer of the Sickle Cell Disease Association of America.
There is no cure for sickle-cell disease, but doctors have gotten much better at managing the condition, Edwards said. Whereas patients often died in their teens back in the 1970s, today it's not unusual for people with sickle-cell disease to live into their 50s. The association estimates that 100,000 Americans have sickle-cell disease.
Another 2.5 million to 3.5 million have sickle-cell trait.
The inherited blood disorder is most common among those of African descent, but it also affects Hispanics and people from Mediterranean countries such as Italy and Greece.
Edwards said the association strongly opposes any suggestion that sickle-cell trait alone puts an athlete at greater risk of dying. She said that, while the group would like to see more research in that area, athletes with sickle-cell trait do not need special considerations beyond the common-sense guidelines that should apply to everyone.
"You need to stay hydrated and have rest periods," Edwards said. "But we don't want to give anyone any reason to think that [someone with sickle-cell trait] should have any restrictions."
There is one important caveat: Those with the trait can pass the errant gene on to their children. And if both parents have it, they have a one-in-four chance of having a child with full-scale sickle-cell disease. That's why African Americans and people in other risk groups are encouraged to find out whether they carry the gene.
Beyond that, Eckman said, those with the trait do not have medical concerns in most circumstances.
One exception may be under extreme physical duress. Eckman said research suggests that exertion, dehydration and heat may trigger the distortion of red blood cells that can impede flow and starve organs of needed oxygen.
But he said that risk is very small and can be reduced even further if athletes take basic precautions by drinking plenty of fluids and not overdoing it. And that's good advice for everyone -- even those without sickle-cell trait.
"Again, this is very rare," Eckman said. "In most cases, a person with sickle-cell trait does not have any symptoms, and they should be able to participate in all sports."
Robyn Shelton can be reached at firstname.lastname@example.org or 407-420-5487.