β + Thalassaemia—Portuguese type: clinical, haematological and molecular studies of a newly defined form of β thalassaemia

Abstract

Summary. We have characterized 14 patients in 10 families with a mild form of homozygous β thalassaemia which has not been previously well defined. As these patients originate from a small area of northern Portugal we propose to call this β+ thalassaemia—Portuguese type. Clinically, the homozygotes range from asymptomatic to thalassaemia intermedia and they are characterized by low levels of HbF, <20%, indicating only a mild deficit in β globin production. Heterozygotes are indistinguishable from those with the more common types of β thalassaemia as regards red cell morphology, haemoglobin analysis and globin chain synthesis studies. Globin gene mapping excluded the presence of α thalassaemia in these patients and demonstrated no abnormalities in the βM‐like globin gene cluster. Restriction enzyme site polymorphisms around the β gene cluster are identical on both chromosomes in all of the homozygotes, confirming their homogeneity.