Clinically, either alone or through their interactions with β-globin structural hemoglobin variants, the β thalassemias are by far the most important forms of thalassemia. Their control and management will pose a major drain on health care resources in the new millennium, particularly in emerging countries in which improvements in sanitation and public health measures have dramatically reduced the number of infant deaths from malnutrition and infection, and hence in which babies with these forms of thalassemia increasingly will survive long enough to present for diagnosis and treatment.
In this chapter we describe the clinical and laboratory features of the severe, transfusion-dependent forms of β thalassemia and their carrier states, and discuss what is known of the diverse family of disorders that fall between these extremes, the β thalassemia intermedias. Readers who wish to learn more about the historical development of this field are referred to the monograph of Weatherall and Clegg. The public health and economic aspects of the thalassemias in the developing countries are discussed in detail by Weatherall et al.
CLASSIFICATION, NOMENCLATURE, AND GENOTYPE/PHENOTYPE RELATIONSHIPS
Despite our increasing knowledge of the molecular pathology of the β thalassemias, it is still useful to retain a broad classification based on their clinical manifestations. The severe, transfusion-dependent forms are designated β thalassemia major, or Cooley anemia, and the symptomless carrier states, thalassemia minor.