Elliptocytose héréditaire

Hereditary elliptocytosis, also known as ovalocytosis, is an inherited blood disorder in which an abnormally large number of the person's red blood cells are elliptical rather than the typical biconcave disc shape. Such morphologically distinctive erythrocytes are sometimes referred to as elliptocytes or ovalocytes. It is one of many red-cell membrane defects. In its severe forms, this disorder predisposes to haemolytic anaemia. Although pathological in humans, elliptocytosis is normal in camelids. RBCs are elleptical in shape rather than normal biconcave shape. Most cases are asymptomatic with abnormalities in their peripherial blood film. A number of genes have been linked to common hereditary elliptocytosis (many involve the same gene as forms of Hereditary spherocytosis, or HS): These mutations have a common end result; they destabilise the cytoskeletal scaffold of cells. This stability is especially important in erythrocytes as they are constantly under the influence of deforming shear forces. As disc-shaped erythrocytes pass through capillaries, which can be 2-3 micrometres wide, they are forced to assume an elliptical shape in order to fit through. Normally, this deformation lasts only as long as a cell is present in a capillary, but in hereditary elliptocytosis the instability of the cytoskeleton means that erythrocytes deformed by passing through a capillary are forever rendered elliptical. These elliptical cells are taken up by the spleen and removed from circulation when they are younger than they would normally be, meaning that the erythrocytes of people with hereditary elliptocytosis have a shorter than average life-span (a normal person's erythrocytes average 120 days or more). EL2 and EL3: The most common genetic defects (present in two-thirds of all cases of hereditary elliptocytosis) are in genes for the polypeptides α-spectrin or β-spectrin. These two polypeptides combine with one another in vivo to form an αβ heterodimer. These αβ heterodimers then combine to form spectrin tetramers.