The great heterogeneity of thalassemia molecular defects in Sicily.

This paper reports the results of 1428 beta-thalassemia chromosomes studied in Sicily during a hemoglobinopathy control program starting in 1983. Molecular screening was performed by direct restriction enzyme analysis, allele specific oligonucleotide (ASO) hybridization, reverse dot blot analysis (RDB) and, for the rare or new mutations, by direct sequencing of polymerase chain reaction (PCR) products. Using these approaches 1410 (98.7%) out of 1428 beta-globin gene defects were characterized, involving 22 different beta-thalassemia mutations. Three of these were present at high frequency (beta(0)39, IVS1, 110 and IVS1,6); the other beta-globin gene defects were found at lower frequency. In the latter, we found a smaller group of mutations at a frequency lower than 10% (IVS1, 1, IVS2, 745, beta S) and a larger one at a frequency lower than 2% [-87, IVS1,2, IVS2,1, fr 6, fr 8 (-AA), fr 44, fr 76, -101, IVS1, 116, IVS1, 3'end G-C, IVS1,5 G-A, IVS1,5 G-C, cod 30, Lepore, delta beta, beta C]. The possible origin of this very large number of mutations is discussed, taking into account the historical point of view. Moreover, this approach has made a first trimester prenatal diagnosis program possible in our region in practically all cases, with a great improvement in general thalassemia management.

Beta A and beta thal DNA haplotypes in Sicily.

A close association between specific restriction fragment polymorphism patterns and specific mutations in Mediterranean people with thalassemia has been demonstrated by Kazazian et al. (1984). This finding is useful to characterize the number and types of mutations in each ethnic group for setting up prenatal diagnosis in the first trimester of pregnancy by the oligonucleotide technique. For this reason we studied 99 beta thal and 46 beta A chromosomes in the Sicilian population. We found seven different cleavage patterns, not considering two new haplotypes so far uncharacterized. Many of the patients (68.3%) were genetic compounds for different haplotypes while only 31.7% were haplotype homozygotes. They may still be thalassemia compound heterozygotes. These findings confirm the molecular basis of the heterogeneity of beta thalassemia in Sicily.

Clinical severity of non-deletion form of HbH disease (--Med/alpha alpha thal).

We carried out alpha-globin gene analysis by restriction endonuclease mapping in a family with 2 cases of HbH disease. These data show that HbH disease in this family results from the interaction between a common deletional defect and a less common non-deletion alpha-thal lesion (--Med/alpha alpha thal). Furthermore, the presence of a beta-thal determinant in this family was investigated by beta gene polymorphism study. We showed that a patient with HbH disease also inherited a beta-thal determinant from the mother and although this was a beta O-thal gene, it was not sufficient to mask the severe alpha chain deficiency. The --Med/alpha alpha thal genotype is more severe than other types of alpha thalassaemia interactions causing HbH disease, probably because the expression of alpha alpha thal determinant may be lower than that of an alpha-thal determinant containing just a single alpha gene (-alpha) and the output so poor that the presence of one beta-thal gene does not significantly change the clinical picture.

alpha alpha alpha anti-4.2 Haplotype and heterozygous beta null thalassemia in a Sicilian family.

The presence of the alpha alpha alpha anti-4.2 haplotype and heterozygous beta null thalassemia in a Sicilian family is described. These findings confirm the presence in Italy of a leftward deletion (-alpha 4.2) and indicate that this may not be rare. Furthermore, although the beta thalassemia determinant in this family has a severe expression, the interaction with the triplicated alpha gene does not necessarily express itself as thalassemia intermedia.