Football players are found to be carriers of sickle cell trait later in life

From 2000 to 2014, nine collegiate football players unexpectedly collapsed and died during training. The cause? Muscle breakdown leading to organ failure. While in top physical shape, these players were later found to be carriers of sickle cell disease, a condition known as sickle cell trait (SCT).

"More student-athletes with sickle cell trait have died than those with any other condition, including heart defects," notes John Wood, MD, PhD, from The Saban Research Institute of Children's Hospital Los Angeles. "Sickle cell trait should not be a barrier to an active lifestyle or competitive sports, but the problem is that many people won't have any warning symptoms. Because of that, they don't even know they have this condition and can't take the necessary precautions."

Because only one abnormal copy of the hemoglobin gene is inherited (instead of two), people with SCT don't exhibit the numerous health complications associated with sickle cell disease. Their one normal gene codes for healthy red blood cells and prevents severe symptoms until faced with extreme conditions of heat, dehydration and exertion—like during the military's basic training or professional sports.

Under these conditions, rapid, painful muscle breakdown can occur, damaging the kidneys and triggering cardiac arrest.

"How sickled hemoglobin in the red blood cell triggers such rapid muscle damage is quite a puzzle," says Wood. "It is also unclear why only a few athletes are stricken when so many others participate under harsh conditions without difficulty. That's what we are trying to find out."

It's estimated that 1 in 12 African-Americans and about two million people in the U.S. have SCT. While sickle cell disease is tested for immediately after birth, few individuals are told if they are positive for SCT because it is not considered to be a life-threatening condition.

But the U.S. Armed Forces and the NCAA are taking matters into their own hands, recently mandating SCT testing in all recruits and Division I and II athletes. With proper knowledge of their condition, individuals with SCT can work with athletic staff and develop a healthy training regimen, eliminating excess risk of sports participation. Proper hydration, graded pre-season training, acclimation to major altitude changes and early recognition of warning signs—such as excessive muscle discomfort or urine discoloration—can prevent catastrophe.

The NFL is also taking notice.

"With funding from NFL Charities, we studied how red blood cells differ in their stiffness and ability to deliver oxygen to the muscle in people with SCT," says Wood. "In fact, we found that individuals with SCT exercised to lower oxygen levels and red cell energy reserves than people with regular hemoglobin. This could allow SCT athletes to unknowingly push their muscles to dangerously low oxygen and energy levels during rigorous activity."

Wood and colleagues are currently expanding on this research and looking into how the body regulates blood flow to the muscles and brain in patients with SCT and in those with sickle cell disease. They believe that this could be the essential factor in determining who's at risk for developing serious complications during vigorous exercise.