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

?-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 -?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 -?3.7/- _SEA. The -? 3.7 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 ??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