The spectrum of β-thalassaemia mutations in Sicily

To characterize β-thalassaemia genes among the Sicilian population we have previously determined the DNA haplotypes in the β-globin gene cluster of 99 β-thal chromosomes. We found seven haplotypes, although 95 of 99 β-thal chromosomes contained framework 1 and framework 3 β genes. We have now determined the mutation in all 99 of these β-thal genes by the use of oligonucleotide hybridization, PCR-amplification and direct genomic sequencing, and direct restriction analysis. Our results indicate that (1) the β°-39 mutation is most frequent (35%): (2) β°-39, IVS-1 nt 110 and IVS-1 nt 6 mutations account for 90% of β-thal genes: (3) the IVS-1 nt 6 mutation is more frequent in thalassaemia intermedia (77%) than in Cooley's disease (34%): (4) the association between haplotypes and specific mutations is imperfect, but mutation spread has occurred within haplotypes containing the same β-gene framework: (5) the β°-39 and the IVS-1 nt 6 mutations, with a mutation spread to two major haplotypes, may be older than the IVS-1 nt 110 mutation: (6) these data make possible first-trimester prenatal diagnosis in many families (85%) in Sicily using only three pairs of oligonucleotides. In addition, a new mutation, a frameshift at codon 76 due to loss of a C residue, was found in a single β-thal chromosome.