A cluster of unexplained deaths of US athletes while exercising could be down to several genes that affect the ability of red blood cells to carry oxygen.
The findings could be turned into a test to see if some people are at greater risk of collapsing on the sports field, says Lorena Madrigal at the University of South Florida.
The sudden death of young athletes is very rare, and is sometimes caused by an unsuspected heart problem, but being a carrier of the gene variant that causes sickle cell anaemia may also be a factor.
Sickle cell anaemia is a genetic disorder that involves having abnormal haemoglobin, the molecule that carries oxygen in red blood cells. Under some conditions, such as physical exertion, these red blood cells can warp into a crescent shape and block blood vessels, causing pain and breathing difficulties.
The disorder is more common in people who have African, Mediterranean and South Asian ancestry, probably because it gives protection from malaria. It was thought that health problems only occur when a person has two copies of sickle cell gene variants, and that carriers – who have only one copy– had no issues.
But some suspect that sickle cell carriers have a higher risk of sudden death during exercise. There have been 23 known cases of this happening to African-American athletes who were carriers, according to a registry of such cases going back 31 years, although we don’t know if this gene was responsible.
Madrigal has been researching whether particular sickle cell carriers may be more susceptible to sudden collapse during exercise. She and her colleagues genetically tested 29 African-American college football players who are sickle cell carriers, and asked them about their health.
They found that people who had previously collapsed during exercise with pain and fatigue were more likely to have one of two additional genetic variants that affect a different haemoglobin gene. The gene is normally active in fetuses, but in some people with sickle cell anaemia it stays active into adulthood and lessens severity of their symptoms.
The team’s work suggests that sickle cell carriers who have less active fetal haemoglobin genes are at a higher risk of health issues during exercise.
Madrigal says further studies may lead to a test that could predict which sickle cell carriers have a higher likelihood of collapsing. “At the moment, there’s no way to predict who’s at risk.”
However, we don’t know if the 23 athletes who died carried any of the variants highlighted by the team’s study.
Simon Dyson of De Montfort University in Leicester, UK, says US colleges should focus on safer training practices, such as avoiding pushing people too hard, and protecting athletes from overheating.
This would be safer for everyone, as even fit and healthy people can die from heat exhaustion during exertion. “Appropriate precautions for all those undertaking exercise can prevent deaths,” says Dyson.
Journal Reference: Southern Medical Journal