Molecular characterization of the - -SEA alpha thalassemia allele in Mexican patients with HbH disease

α-thalassemia is one of the most prevalent hemoglobin disorders in the world, in south-east asians, the--sea allele is widely found in the hbh disease patients. the purpose of this work is to describe the molecular characteristics of hemoglobin h disease in three patients from two mexican families, as well to analyze the dna sequence of the --sea allele to determine the precise site of the crossover. the -α3.7 and --sea alleles were identified using an established long-pcr method modified in our laboratory. the crossover site of --sea mutation was analyzed by dna sequencing. the three hbh subjects showed the same genotype -α3.7/--sea. the -α3.7 allele has been observed in almost every racial studied group, whereas the --sea allele is predominant in south-east asian countries. dna analysis through the breakpoint sites of the --sea allele in both families showed the 5' breakpoint at the third base of codon 28 in the ψα2 gene and the 3' breakpoint within an alu-jo sequence, 1,328 nucleotides upstream of the 3'hvr. therefore the size of the deletion is 19,303 nucleotides. this is the first report in which the flanking deletion sites of the--sea mutation have been analyzed in mexican patients, the 5' and 3' ends of the deletion is well determined.