par Gulbis, Béatrice ;Cotton, Frédéric ;Vertongen, Françoise
Référence Encyclopédie médico-chirurgicale. Hématologie
Publication Publié, 2011
Article révisé par les pairs
Résumé : Hemoglobinopathies are genetic disorders of hemoglobin and are the most common inherited disorder in humans. The hemoglobin molecule is composed of four separate polypeptide chains, two alpha and two beta, as well as four iron-bearing heme groups that bind oxygen. The alpha chains are coded for by two similar genes on chromosome 16, the beta chains being coded by a single gene on chromosome 11. If most commonly, there is no structural or functional consequence, alteration of a single amino acid may have dramatic clinical consequences. This is the case with several unstable hemoglobins with high oxygen affinity or M hemoglobins. Depending on the molecular defect, unstable hemoglobins may induce hemolysis in vivo, hemoglobins with high affinity may induce compensatory erythrocytosis and hemoglobin M always cause pseudo cyanosis more or less visible. Generally, the molecular defect explains the pathology: unstable hemoglobins are frequently due to mutations in the heme pocket, hemoglobins with high affinity to mutations that alter the transition in the three-dimensional hemoglobin conformation that accompanies the removal of oxygen and M hemoglobins to mutations that stabilize the heme-iron in its oxidized form. Diagnosis of these rare hemoglobin variants is mandatory for adequate treatment, or in the case of hemoglobin M and hemoglobin with high affinity to prevent inappropriate investigations due to the mistaken impression that the patient has a cardiac, pulmonary or neoplastic disorder. © 2004 Elsevier SAS. Tous droits réservés.