To determine the incidence of delta(+)27 thalassaemia in Northern Sard
inia we examined blood samples from 750 Sardinian schoolboys by PCR-ba
sed molecular analysis. The incidence of delta(+)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 beta-thalassaemia is 10
.5% and their interaction has been calculated at 0.0003. The majority
of delta(+)27 carriers are characterized by a HbA(2) level lower than
1.9% and the mean HbA(2) level is significantly lower than in normal s
ubjects. All compound heterozygotes for delta(+)27 and beta-thalassaem
ia show a silent beta-thalassaemic phenotype related to normalization
of their HbA(2) levels. This study suggests that delta(+)27 thalassaem
ia should be borne in mind in counselling at-risk couples in which one
member has the typical high HbA(2) beta-thal trait while the other sh
ows normal or borderline HbA(2) level. In these subjects, PCR-based EC
O O 109 I digestion of the delta globin gene allows rapid detection of
the delta(+)27 mutation.