Hematological Diagnosis of B Thalassemia Mutations

Beta thalassemia, the most common disease inherited at a single genetic locus, is a major cause of morbidity and mortality in populations having high frequencies of the beta-thalassemia mutations. At this juncture, the mainstays of therapy in afflicted populations consist of population screening, genetic counseling, and prenatal diagnosis. Accurate diagnosis, on which each of these depends, entails detecting at the DNA level beta-thalassemia mutations, which are both numerous and of diverse ethnic distribution. Practical diagnosis of beta-thalassemia mutation in distinct ethnic groups requires both accuracy and a level of simplicity that can be applied outside dedicated research laboratories. We will use the polymerase chain reaction (PCR)-based Reverse Dot Blot method to develop diagnostic kits for the beta-thalassemia mutations found commonly in Southeast Asian and in African-American populations. The Reverse Dot Blot method is sensitive because it employs PCR to amplify 100,000 to 1,000,000 times the genes to be tested, accurate because it depends on the same Watson- Crick base pairing that insures faithful transmission of genes from one generation to the next, and efficient because it tests amplified gene target sequences for the presence of several mutations in a single hybridization reaction. We will design oligonucleotide probes complementary to the beta-thalassemia mutations segregating in defined populations and to their allelic wild-type sequences, fix these probe pairs to filters, amplify and label target DNA to be tested, and determine if the test DNA contains mutant beta-thalassemia sequences by whether it hybridizes to fixed mutant probes or only to wild type probes. Diagnostic kits designed using this method will be applied to the rapid, accurate diagnosis of beta-thalassemia, which will greatly facilitate screening, counseling, and prenatal diagnosis in popula- tions at risk.