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Sickle cell anemia
Sickle cell anemias are chronic hemolytic diseases that may induce three types of acute accidents: severe anemia, severe bacterial infections, and ischemic vasoocclusive accidents (VOA) caused by sickle-shaped red blood cells obstructing small blood vessels and capillaries. Many diverse complications can occur.
ORPHA:232Classification level: Disorder
The prevalence of sickle cell carriers in 25 European states is estimated at about 1/150. In central and western Africa (15-25%), in the French West Indies (10-15%) and in Mediterranean areas (1-15%) a high prevalence is observed in areas that are or have been affected by malaria, because the trait offers protection against pernicious malaria.
The presence of fetal hemoglobin means that the disease doesn't manifest until after 3 months. Clinical manifestations are extremely variable between individuals and at different times. In addition to anemia and bacterial infections, VOAs cause hyperalgic focal ischemia (and sometimes infarction) when they occur in the muscles or skeleton. Over the course of time, VOAs may compromise the integrity of tissues or organs.
Sickle cell anemia is determined by combinations of two abnormal alleles of the beta globin gene among which at least one carries the beta 6 glu-val mutation (Hb S). Individuals who carry the gene for hemoglobin S and the gene for thalassemia beta are affected by thalassodrepanocytosis. The betaS/betaC (beta 6 glu-lys) form is also frequent.
Diagnosis is based on analysis of hemoglobin using isoelectric focusing, by HPLC, solubility test (Itano test) and molecular analysis. Screening of healthy carriers by family or by population can be suggested and requires prospective genetic counseling.
Differential diagnoses include other hereditary hemolytic diseases.
Prenatal diagnosis is possible, after genetic counseling, by molecular analysis of a sample of chorionic villi or amniotic fluid.
Transmission is autosomal recessive.
Management and treatment
From birth, management should integrate prevention of infections, pain and eventual complications, with social and psycho-educational support, within multidisciplinary centers that are equipped with intensive care (immediate access to blood transfusion). An orphan drug based on hydroxycarbamide (hydroxyurea) has obtained European marketing authorization for the severe forms of the disease. Regular or occasional transfusions remain an essential therapeutic method. Bone marrow transplantation is indicated in cases with cerebral vasculopathy.
The prognosis is difficult to predict. Serious VOA or organ failure can be a cause of death.