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

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Abstract
Patients (14) in 10 families with a mild form of homozygous .beta. thalassemia which has not been previously well defined were characterized. As these patients originate from a small area of northern Portugal this was called .beta.+ thalassemia, Portuguese type. Clinically, the homozygotes range from asymptomatic to thalassemia intermedia and they are characterized by low levels of HbF, < 20%, indicating only a mild deficit in .beta. globin production. Heterozygotes are indistinguishable from those with the more common types of .beta. thalassemia as regards red cell morphology, Hb analysis and globin chain synthesis studies. Globin gene mapping excluded the presence of .alpha. thalassemia in these patients and demonstrated no abnormalities in the .beta.-like globin gene cluster. Restriction enzyme site polymorphisms around the .beta. gene cluster are identical on both chromosomes in all of the homozygotes, confirming their homogeneity.