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The beta-thalassemia syndromes are a heterogeneous group of genetic disorders characterized by reduced or absent expression of the beta-globin gene. To date, over 300 beta-thalassemia alleles have been characterized in or around the beta-globin region. Thalassemia major is severe anemia necessitating chronic blood transfusions, splenectomy, iron chelation therapy, and bone marrow transplantation. Usually thalassemia major results from homozygosity or compound heterozygosity for severe betaO- and/or beta+-thalassemia mutations. Thalassemia intermedia is a clinical diagnosis that describes a symptomatic but less severe condition than beta-thalassemia major. beta-thalassemia intermedia may arise from several different combinations of alpha- and/or beta-thalassemia mutations. Heterozygous beta-thalassemia is typically characterized by a mild microcytic hypochromic anemia without any significant clinical implications. In this report, we describe a 63-year-old Africian American woman with asymptomatic homozygous beta-thalassemia, who seems to carry 2 copies of the -29 mutation in the promoter region of the beta-globin gene. Her elevated hemoglobin F level of 83% was associated with heterozygosity for the Xmn I polymorphism upstream of the Ggamma-globin gene. Southern blot analysis at the alpha-globin locus did not show any deletion that would account for the mildness of her phenotype. Therefore, homozygosity for the -29 mutation along with the Xmn I polymorphism appears to confer an extremely mild beta-thalassemia phenotype. This observation has important implications in the prenatal diagnosis and genetic counseling of families segregating this type of genetic defect.

We have optimized a battery of reverse dot blot oligonucleotide probes for detecting the most common beta-globin gene mutations in Asians and American Blacks. These probes allow a high degree of coverage of mutant chromosomes in these two populations and are useful in mutation screening and prenatal diagnosis. When coupled with the Mediterranean subset of probes, a 95% worldwide coverage of beta-thalassemia mutations should be possible. The use of these probes in the reverse dot blot system should allow the distribution of premade strips and application to automated screening.

The molecular lesions causing beta-thalassemia in Sicily can be subdivided into two groups. One that occurs at a 71% frequency and consists of the beta 39, IVS 1,110 and IVS 1,6 mutations and the other group at a 20% frequency comprising the -87, beta s, IVS 1,1 and IVS 2,745 mutations. The identification of all these mutations by polymerase chain reaction (PCR) and conventional dot-blot hybridization has been time consuming and expensive. In this article, we describe the implementation of the reverse dot-blot (RDB) hybridization as a rapid nonradioactive method for the identification of the nine most frequent molecular lesions in the beta-globin gene (-87, beta s, beta c, IVS 1,1, IVS 1,6, IVS 1,110, beta 39, IVS 2,1, IVS 2,745) in Sicily. Sixty prenatal diagnoses were performed by this RDB assay, each of which was confirmed by dot-blot/ASO hybridization; thus demonstrating the accuracy of the RDB. The main advantage of this assay is the rapid typing of an individual's DNA for many mutations in a single working day. Because the mutations in this assay are representative for the Mediterranean region, this mutational panel can also be extended to the screening of beta-thalassemia from other Mediterranean regions.