Sickle cell trait describes a condition in which a person has one abnormal allele of the hemoglobin beta gene (is heterozygous), but does not display the severe symptoms of sickle cell disease that occur in a person who has two copies of that allele (is homozygous). Those who are heterozygous for the sickle cell allele produce both normal and abnormal hemoglobin (the two alleles are codominant with respect to the actual concentration of hemoglobin in the circulating cells). Sickle cell disease is a blood disorder wherein there is a single amino acid substitution in the hemoglobin protein of the red blood cells, which causes these cells to assume a sickle shape, especially when under low oxygen tension. Sickling and sickle cell disease also confer some resistance to malaria parasitization of red blood cells, so that individuals with sickle-cell trait (heterozygotes) have a selective advantage in environments where malaria is present. Symptoms and signs
Sickle cell trait is a hemoglobin genotype AS and is generally regarded as a benign condition. However, individuals with sickle cell trait may have rare complications. For example, in November 2010, Dr. Jeffery K. Taubenberger of the National Institutes of Health discovered the earliest proof of sickle-cell disease while looking for the virus of the 1918 flu during the autopsy of an African-American soldier. Taubenbergers autopsy results showed that the soldier had had a sickle-cell crisis that contributed to his death even though he had only one copy of the gene.
Sickle cell variants descended from this ancestral haplotype comprise five haplotypes named after toponyms or ethnolinguistic groups (the Arabian/Indian, Benin, Cameroon, Central African Republic/Bantu, and Senegal variants), and another designation earmarked for atypical sickle-cell haplotypes. Their clinical importance is because some are associated with higher HbF levels (e.g., Senegal and Saudi-Asian variants tend to have milder disease). In athletes
In some cases, athletes with sickle cell trait do not achieve the same level of performance as elite athletes with normal hemoglobin (AA). Athletes with sickle cell trait and their instructors must be aware of the dangers of the condition during anaerobic exertion especially in hot and dehydrated conditions. In rare cases, exercise-induced dehydration or exhaustion may cause healthy red blood cells to turn sickle-shaped, which can cause death during sporting activities.While more research is necessary on the topic, the correlation found between individuals with sickle cell trait and an increased risk of sudden death appears to be related to microcirculatory disorders, during exercise. In recent years the NCAA has partnered with the ACSM and issued a joint statement, warning athletes about both the prevalence and the potential risk factors of sickle cell trait.