The first illustration shows two parents who have sickle cell trait (AS) and the chances that they will have a child with normal hemoglobin (AA) which is (1:4) 1 in 4 or 25%, sickle cell trait which is (2:4) 2 in 4 or 50%, or sickle cell disease (SS) which is (1:4) 1 in 4 or 25%.
The second illustration shows that if one parent has S trait and one parent has C trait then there is a (1:4) 1 in 4 or 25% chance each of AA, AC, AS, SC. Only SC causes sickle cell disease.
The third illustration shows that if one parent has the disease (SS) and one has the trait (AS) then they have a 50% chance of having a child with the trait or disease.
The fourth illustration shows that if one parent has normal hemoglobin and the other has sickle cell trait then none of their children will have the disease.
The fifth illustration shows that if one parent has sickle cell disease (SS) and one parent has normal hemoglobin, then all of their children will have sickle cell trait, and none will have the disease.
This is the risk with each pregnancy. So, it is possible to have three or more consecutive pregnancies with normal hemoglobin or three or more with sickle cell disease even though the chances of this are small.
Sickle cell trait is not a disease, but it is a risk factor for some medical problems. Risk means that you may or may not develop the problems that are reported to occur. Under extreme conditions, people who have sickle cell trait can have “sickling” of their red blood cells. One of the most severe of these conditions is called exertional rhabdomyolysis and occurs during very strenuous exercise with dehydration, leading to an increase in body temperature and sickling in the kidneys and other organs. This has occurred in military recruits and in college sports, notably football. Under these conditions, the sickling of the red cells in the kidneys and muscles causes renal failure and can lead to death. The military has taken steps to increase hydration (liberal amounts of water) and add rest periods in the heat. Currently, there is no increased risk of exertional rhabdomyolysis in military recruits with sickle cell trait compared to those without sickle cell trait due to these simple changes.
At high altitudes with low oxygen, there can be sickling within the spleen causing pain in the upper left side of the abdomen and sometimes nausea. Splenic infarcts are a separate problem and not related to exertional rhabdomyolysis. Splenic infarcts can be serious and need to be evaluated, they do not always require treatment but can lead to serious problems such as splenic rupture with significant blood loss and other less common complications. With exercise at a high altitude, a splenic infarct can occur in anyone who has sickle cell trait. Flying in commercial pressurized airplanes does not pose a problem as long as there is good hydration.
Besides the risk of exertional rhabdomyolysis and splenic infarction at high elevations with exercise, there is an increased risk of some other medical problems such as chronic kidney disease – which can occur in adults. There is a slight increase in blood clots (embolism) in the extremities and lungs particularly during surgery, and an extremely rare type of kidney cancer called renal medullary carcinoma.
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