Sickle cell trait may not increase mortality risk

By Sally Robertson, B.Sc.Aug 4 2016

People who carry a gene for sickle cell disease do not appear to be at an increased risk of premature death, according to a study by researchers from Stanford University School of Medicine.

Sickle cell disease is an inherited blood disorder that occurs in 1 out of every 365 individuals born in America. People with this condition have hard, sticky and sickle-shaped red blood cells, which causes long term bouts of severe pain and dramatically shortens lifespan.

People who have this condition carry two copies of the gene for sickle cell disease. Those who carry only one copy of the gene variant are said to have sickle cell trait, which occurs in about 1 in 13 African-Americans.

Health experts have long believed that having sickle cell trait increases the risk of premature death, but the new study challenges this notion and comes to a different conclusion.

Previous studies have suggested that sickle cell trait is associated with dire health consequences, including an increased risk of mortality due to a potentially fatal condition called exertional rhabdomyolysis (ER). ER occurs when the breakdown products of damaged muscle tissue build up in the blood and kidneys.

It has been known to affect footballers, often as a result of too much physical exertion in extreme temperatures and without drinking water. ER has also been shown to be a risk among soldiers on active duty.

This risk means that the Army, Navy and NCAA all now screen for sickle cell trait and people who are found to have the condition are warned about overheating and dehydration.

However, in the first longitudinal cohort study of sickle cell trait among African-American soldiers, Lianne Kurina (Stanford) and colleagues have shown that there is no increased risk of death associated with sickle cell trait.

As reported in the New England Journal of Medicine, the team analyzed health records of 47,944 African-American soldiers for whom sickle cell trait status was known and who served on active duty between 2011 and 2014.

The team found that the risk of ER was only 54% higher among soldiers with sickle cell trait than among those without it. Although this may sound like a big increase, it is far smaller than the 300% increased risk associated with the use of some ordinary prescription drugs. The increased risk associated with sickle trait is, in fact, similar to that incurred by increasing age, obesity and smoking.

Kurina says the difference between her team’s study and previous ones may be the better safety regulations nowadays for soldiers on active duty. Since 2003, soldiers who exercise strenuously have been required to build up their exercise gradually, keep themselves well hydrated and to rest regularly when it is hot. According to the study, all of these measures reduce exercise-related deaths, irrespective of sickle cell trait status.

"Under conditions of universal precautions against dehydration and overheating, we don't see an elevation in the risk of mortality in people with sickle cell trait," says Kurina, who thinks that the study's results call into question whether screening service members with sickle cell trait is actually necessary.