sickle trait

Monday, January 9, 2012

People can dream but their road to success can be derailed in the most unusual ways, perhaps none as strange as that which affected Ryan Clark of the Pittsburgh Steelers. The team played this weekend in Denver, the Mile High City, so named because it sits at an altitude of 5280 feet. The last time Clark played in Denver, he ended up critically ill requiring emergency surgery because of his genetics; he suffers from sickle trait, a condition that affects the shape and function of red blood cells. So while his teammates competed, Clark was relegated to the sidelines.

Red blood cells are manufactured in the bone marrow and take their unique biconcave shape (think of squeezing a marshmallow between your fingers) to increase storage capacity for hemoglobin molecules that carry oxygen and also to make the cells pliable and soft so they can squeeze through the tiniest blood vessels in the body. In sickle disease, the red blood cells form an abnormal crescent shape that is rigid, causing the red cells to be damaged. As well, the cells aren’t malleable enough to get through tight spaces and this can increase the risk of forming small blood clots in the small capillaries of different organs causing the potential for organ damage.

Sickle cell disease is a genetic disease that most commonly affects people whose heritage is usually African and Caribbean. Patients with full blown sickle cell anemia have inherited a sickle gene from each parent and are usually diagnosed in childhood as having this autosomal recessive disease. Autosomal meaning that the gene isn’t located on the X or Y sex chromosome. Recessive means that you need to have two negative genes to have the disease. If only one parent passes on that “bad” gene” the disease may not be present at or, or in the case of sickle disease, the patient has sickle trait. Sickle trait patients usually live normal lives and have very few if any symptoms. Unfortunately, that is not always the case.

In the US, full blown sickle cell anemia affects about 100,000 people but almost 2 million more have the sickle trait. In sickle trait, symptoms rarely occur but usually are brought on by exercise, presumable because of lactic acid production as the body moves from aerobic to anaerobic production. This may be why Mr. Clark became ill playing football in Denver. There is less oxygen available in the air at altitude and the intense exercise and dehydration caused his normally shaped red cells to morph into the sickle shape.

Perhaps one of the most affected organs of the body in sickle disease is the spleen whose job it is to filter the blood, get rid of debris and to remove damaged red cells. Sickled red cells clog up the filter system and can cause the spleen to acutely enlarge, swell with blood and cause shock. As well, a variety of other organs can be involved, most often causing a pain crisis because blood supply is interrupted when the sickle cells obstruct the small capillary blood vessels, but catastrophes like stroke, loss of vision and kidney failure among other complications can occur. There are too many to document complications but commonly in sickle disease, spleen function is gradually lost as blood vessels clot off and the spleen dies or infarcts. Its role in the immune system is also lost and immunizations may be needed to fight off common causes of infection, especially the pneumococcus bacteria. This same immunization is also given to any patient who has needed a splenectomy (an operation to remove the spleen).

Sickle trait is spared any symptoms unless one is unlucky enough, because of unusual circumstances, to have normal red cells change into sickled ones. The risk of sickle trait in athletes is well recognized. After the death of a college athlete in 2006, the NCAA began recommending testing of all athletes whose sickle status was not known (most states test newborns routinely). If sickle trait is present, adjustments in the training programs can allow the athlete to reach his or her full potential. Taking a few extra seconds to recover between sprints or repetitive training and having oxygen supplementation on the sidelines and at practice can decrease the buildup of lactic acid and minimize the risk of sickling.

Because he had failed a trial of fire with his first game at altitude in 2007, Mr. Clark sat on the sidelines this weekend. His story is a reminder that while a person may appear fit, there is always potential danger that lurks under the surface. There is a common theme that reasserts itself in medicine and in life; prevention is easier than dealing with disaster.

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