Sickle cell trait
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| Sickle cell trait Classification and external resources |
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| ICD-10 | D57.3 |
|---|---|
| OMIM | 603903 |
| MedlinePlus | 000527 |
| eMedicine | topic list |
Sickle cell trait describes the way a person can inherit one of the genes of sickle cell disease, but not develop recurrent symptoms. Sickle cell disease is a blood disorder in which the body produces an abnormal type of the oxygen-carrying substance hemoglobin in the red blood cells. Sickling and sickle cell disease is an adaptive evolutionary response to reduce malaria parasitization of red blood cells.
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[edit] Sickle haemoglobin
Normal hemoglobin is called hemoglobin A, but people with sickle cell disease have only hemoglobin S, which turns normal, round red blood cells into abnormally curved (sickle) shapes.
Normally, a person inherits two genes (one from each parent) that produce beta-globin, a protein needed to produce normal hemoglobin (hemoglobin A). A person with sickle cell trait inherits one normal beta-globin gene (hemoglobin A) and one defective gene (hemoglobin S).
[edit] Prevalence
Sickle cell trait prevalence is highest in West Africa ( 25%) of the population. However, it has been described globally in Caucasians in Mediterranean countries of Italy, Greece, and Spain. It has been described Turks, North Africa, Iranians, Arabs, Middle Eastern nations including Iran, and in Indians.
One out of every ten African- Americans have sickle cell trait.
[edit] Symptoms
Sickle cell trait (Hemoglobin genotype AS) is not benign. People with sickle cell trait have symptoms due to co-morbidity and conditions which may cause heat, dehydration, hypoxemia, and sickling. There have been reports of pulmonary venous thromboembolism in pregnant women with sickle cell trait,[1] or men during prolonged airflight, mild strokes and abnormalities on PET scans in children with the trait, complicated migraine headaches,[2] poor urinary concentrating ability, increased incidence of renal carcinoma, sudden deaths during physical exertion in US black army recruits, and during police chase of black suspects,[3][4] splenic infarcts at high altitude, even in white patients with the trait. However, they can pass the sickle cell trait to their children, and in rare cases, exercise-induced dehydration or exhaustion can cause healthy red blood cells to turn sickle-shaped, which can cause death during sporting activities.[5] There have been calls to reclassify sickle cell trait as a disease state, based on its malignant clinical presentations.[6] Sickle cell trait appears to worsen the complications seen in diabetes mellitus type 2 (retinopathy, nephropathy and proteinuria)[7] and provoke hyperosmolar diabetic coma nephropathy) especially in male patients. 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.
A person in whom both beta-globin genes are abnormal (they produce hemoglobin S) has sickle cell disease, which can cause serious problems. Both parents must have either the sickle cell trait or the disease itself for a child to have sickle cell disease. Genetic/prenatal counselling is available to reduce the incidence of Hemoglobin SS conceptus.
People who have the sickle cell trait have reduced susceptibility to cerebral malaria, due to natural selection for the heterozygote advantage. This is called 'balanced polymorphism" where a deleterious gene confers a survival advantage. However, people with the sickle cell trait can still contract severe cases of malaria.
[edit] References
- ^ Austin H, Key NS, Benson JM, et al (August 2007). "Sickle cell trait and the risk of venous thromboembolism among blacks". Blood 110 (3): 908–12. doi:. PMID 17409269.
- ^ Osuntokun BO, Osuntokun O (June 1972). "Complicated migraine and Haemoglobin AS in Nigerians". Br Med J 2 (5814): 621–2. PMID 5031686. Full text at PMC: 5031686.
- ^ Kark JA, Posey DM, Schumacher HR, Ruehle CJ (September 1987). "Sickle-cell trait as a risk factor for sudden death in physical training". N. Engl. J. Med. 317 (13): 781–7. PMID 3627196.
- ^ Mitchell BL (March 2007). "Sickle cell trait and sudden death--bringing it home". J Natl Med Assoc 99 (3): 300–5. PMID 17393956.
- ^ Eichner ER (August 2007). "Sickle cell trait". J Sport Rehabil 16 (3): 197–203. PMID 17923725.
- ^ Ajayi AA (October 2005). "Should the sickle cell trait be reclassified as a disease state?". Eur. J. Intern. Med. 16 (6): 463. doi:. PMID 16198915.
- ^ Ajayi AA, Kolawole BA (August 2004). "Sickle cell trait and gender influence type 2 diabetic complications in African patients". Eur. J. Intern. Med. 15 (5): 312–315. doi:. PMID 15450989.
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