ABSTRACT
Alpha-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 -alpha 3.7 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 -alpha3.7/--SEA. The -alpha3.7 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 psi alpha 2 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.
