The gene encoding the I blood group antigen: review of an I for an eye.
Unlike most blood group antigen pairs, the I and i antigens are not antithetical (produced by allelic pairs) but, rather, they are reciprocal. The I antigen is formed by the action of an enzyme (a glycosyltransferase), which adds branches onto the i antigen. Thus, branched I antigen is formed at the expense of its precursor, the linear i antigen. The antigens are present on all blood cells and have a wide tissue distribution. Soluble I antigen is found in milk, saliva, and amniotic fluid, and a small amount is in plasma. The function of these antigens is unknown but the I antigen has a decreased expression and the i antigen has a concomitant increased expression in conditions that result in increased hematopoiesis. The gene encoding the branching transferase has been cloned and sequenced, and the mechanism underlying the i adult phenotype with and without association with cataracts has been elucidated.
Reid
M E
ME
Immunochemistry Laboratory, New York Blood Center, 310 East 67th Street, New York, NY 10021, USA.
D002240:Carbohydrate Sequence; D002386:Cataract / Q000151:congenital / Q000209:etiology / Q000276:immunology*; D016695:Glycosyltransferases / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D006801:Humans; D007048:I Blood-Group System / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D014018:Tissue Distribution
D007048:I Blood-Group System; D016695:Glycosyltransferases