Foto de stock - DREPANOCYTEMIA, DRAWING<BR> <BR>Genetic risks to declare sickle-cell anemia. Sick-cell anemia, is a chronic hemolytic anemia. This congenital disease due to the production of an abnormal protein of hemoglobin (hemoglobin S or Hb S), less soluble. This one agregates, and is responsible for the deformation of the red blood corpuscles that take a very recognizable shape in sickle (sickle cells). Thoses red blood corpuscles are rigidified and have lost their capacity to warp, that they cause an occlusion of the blood vessels of smaller caliber, as a consequence ischemic accidents. Recognized as abnormal by the organism, thoses red blood corpuscles are destroyed in the spleen causing a regenerative anemia. This hemoglobinopathy affect mainly populations of Africa. Sickle-cell anemia is transmitted hereditarily according to the recessive autosomic mode. This means that the two parents must be bearer of at least a copy of the abnormal gene so that their child have a risk out of four to be ill (bearer of the two copies of the abnormal gene). Indeed, the genome of each individual contain two copies (or alleles) of each gene , then it can be zero, one or two copies of the gene responsible for the disease. A person bearing two identical alleles is called homozygote, whereas a person bearing two different alleles is called heterozygote. During the conception of the child, each of the two parents transmit one of their two alleles to the child (one in the oocyte, the other in the spermatozoon). If both parents have the two alleles normal (homozygotes NN), they transmit a normal allele each (N) and the child will be healthy (genotype NN). If one of the two parents is a healthy bearer of the disease (heterozygote NP), that is he bears a normal and an abnormal allele, the child will have one risk out of two to be himself healthy bearer of the disease (genotype NP) and one chance out of two not to be affected (genotype NN). A healthy bearer can transmit the disease but he is not affected himself. If both parents are healthy bearers (NP), the child has one risk out of four to be affected by sickle-cell anemia (genotype homozygote PP), two risks out of four to be healthy bearer (NP) and only one chance out of four not to be affected (NN). Nowadays, genetic tests enable to detect healthy bearers in predisposed families, and then to evaluate the risk for the child to be born affected by the disease.