Molecular basis for HbH disease in Italy: geographical distribution of deletional and nondeletional alpha-thalassemia haplotypes.

We have investigated the molecular basis for HbH disease in 16 patients from Sardinia, and central and southern Italy. We have shown that HbH disease is produced by the interaction of at least 10 different deletional or nondeletional alpha-thalassemia haplotypes, some of which have been already described in the Mediterranean area (--Med,-(alpha)20.5,-alpha 3.7 type I,-alpha 3.7 type II, alpha 2 NcoI alpha 1, alpha 2 HphI alpha 1). Among the new mutations found in the course of our study, there is a complete deletion of the zeta-alpha cluster and three nondeletional determinants (alpha alpha T), affecting to various extents alpha-globin gene expression. The different alpha-thalassemia haplotypes are not evenly distributed throughout the country. Two alpha 0 determinants [-(alpha)20.5 and the complete deletion of the zeta-alpha cluster] and four alpha + determinants (-alpha 3.7 type II, three nondeletional alpha alpha T mutations) are found exclusively in southern Italy.