Molecular screening and fetal diagnosis of β-thalassemia in the Italian population

This paper reports our experience of molecular screening and fetal diagnosis of β-thalassemia in 457 at risk couples of Italian descent. Molecular screening was carried out by dot blot analysis on amplified DNA with oligonucleotide probes complementary to the eight most common mutations in Italians [β∘39 (C→T); ∘6 (-A); β+-87 (C→G); β+ IVSI nt 110 (G→A); β∘IVSI nt 1 (G→A); β+ IVSI nt 6 (T→C); β∘ IVSII nt 1 (G→A); β+ IVSII nt 745 (C→G)]. By using this approach, we have been able to define the mutation in 92.8% of cases. The rest (all but four) were defined by direct sequencing and this led to the detection of nine rare mutations [β∘76 (-C); β+ IVSI nt 5 (G→A); β+ IVSI nt 5 (G→C); β+ IVSI -1 (cod 30) (G→C); β+-87 (C→T), β∘-290 bp del.; β+-101 (C→T)], and to the characterization of a novel mutation consisting of the deletion of the G at the invariant AG of the IVSII splice acceptor site of the β-globin gene (β IVSII nt 850-1 bp). In the remaining four cases, the β-globin gene showed entirely normal sequences and the β-globin gene cluster was intact, as indicated by Southern blot analysis. Fetal diagnosis was carried out by dot blot analysis with the oligonucleotide probes defined in the parents. The procedure is simple and reliable, and the results can be obtained within 1 week of sampling. No misdiagnosis has so far occurred. The results indicate that fetal diagnosis of β-thalassemia by DNA analysis may be obtained in practically all cases (even in a population showing marked heterogeneity of β-thalassemia) by the combination of dot blot analysis for detecting common mutations, and direct sequencing for defining those that are uncommon.