Climbing Mount Everest or crossing the Sahara by camel? Maybe, you’ve secretly dreamed of doing one of these things? Or, perhaps you’ve made a New Year’s resolution to be more active and get more exercise? Physical activity is key to healthy living, but too much of it might not be a good thing for individuals with certain changes in the HBB gene. In fact, exercise in individuals with these genetic changes could put them at risk. Specific mutations in the HBB gene cause sickle cell disease; an inherited blood disorder and one of the most common genetic diseases in the world.
Normal adult hemoglobin is a protein in red blood cells that carries oxygen. It is made of two smaller proteins; α-globin and β-globin. Sickle cell disease is caused by genetic changes in the HBB gene that encodes β-globin. People with sickle cell disease produce abnormal hemoglobin proteins that clump inside red blood cells, making them sickle shaped, hard and sticky. These red blood cells stick to blood vessels, clogging them, and cutting off the oxygen supply to organs and tissue. When this happens, people with sickle cell disease experience a condition known as an “extreme pain crisis” and may need to be hospitalized. The sickle-shaped red blood cells also tend to burst more easily, because they lack the flexibility of normal red blood cells. This results in a second hallmark symptom of sickle cell disease – anemia or lower levels of red blood cells.
Approximately 300 million people around the world either have sickle cell disease or the sickle cell trait. The sickle cell trait refers to carriers that have one defective copy of the HBB gene and one normal copy of the HBB gene. Carriers can still produce enough normal hemoglobin, so they typically don’t show any symptoms. However, carriers are at a high risk of developing symptoms of anemia under extreme conditions of physical assertion, dehydration and high altitude.
Studies of military personnel in the US show an alarming 30-fold greater risk of sudden death if a person has the sickle cell trait (i.e. carries one abnormal HBB gene). Several cases of exercise-induced deaths of athletes with the sickle cell trait have also been reported in the US. The NCAA (National Collegiate Athletic Association) now requires a mandatory screening for the sickle cell trait in athletes who participate in college sports. Given that 1 in 12 African-Americans, 1 in 50 Asians and 1 in 150 Europeans have the sickle cell trait, this just may be a good preventative measure.
Living with sickle cell disease can be difficult. Many things like high altitude, extreme temperatures, physical activity and dehydration can trigger pain crises. Although nothing is impossible living with sickle cell disease, as proven to us by the Jazz musician Miles Davis and the former NFL running back Tiki Barber.
While sickle cell disease receives much deserved attention, the dangers of inheriting the sickle cell trait tend to be ignored. A carrier for sickle cell disease is not only at risk of having children with sickle cell disease, but they themselves are at higher risk for experiencing symptoms of the disease under certain conditions. The next time you decide to run that half-marathon or do the CN tower climb, you might first want to find out whether you might have the sickle cell trait. Being informed is the best possible strategy because it will minimize your risks, help you practice prevention, and most of all, keep you safe.