Frequency of δ⁺27-thalassaemia in Sardinians

Summary To determine the incidence of δ+27 thalassaemia in Northern Sardinia we examined blood samples from 750 Sardinian schoolboys by PCR-based molecular analysis. The incidence of δ+27 mutation was 1.2% in this study, i.e. twice as high as previously described on the basis of phenotypical studies; the frequency of the β-thalassaemia is 10.5% and their interaction has been calculated at 0.0003. The majority of δ+27 carriers are characterized by a HbA2 level lower than 1.9% and the mean HbA2 level is significantly lower than in normal subjects. All compound heterozygotes for δ+27 and β-thalassaemia show a silent β-thalassaemic phenotype related to normalization of their HbA2 levels. This study suggests that δ+27 thalassaemia should be borne in mind in counselling at-risk couples in which one member has the typical high HbA2 β-thal trait while the other shows normal or borderline HbA2 level. In these subjects, PCR-based ECO O 109 I digestion of the δ globin gene allows rapid detection of the δ+27 mutation.