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.
Subject(s)
Hemoglobin H/genetics , alpha-Thalassemia/genetics , Alleles , Child , DNA Mutational Analysis , Female , Humans , Male , Mexico , Polymerase Chain ReactionABSTRACT
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.
La Talasemia-α es uno de los desórdenes de la hemoglobina más prevalences en el mundo. En el sureste de Asia, --SEA es el alelo más frecuente en pacientes con enfermedad por HbH (EHbH). En el presente trabajo se describen las características moleculares de tres pacientes con EHbH de dos familias mexicanas, y se analiza la secuencia de DNA del alelo --SEA, para determinar los sitios de ruptura. Los alelos -α3.7y --SEA se identificaron por un método de PCR modificado en nuestro laboratorio y los sitios de ruptura por secuenciación de DNA. Los tres pacientes con EHbH mostraron el genotipo -a3.7/--SEA. El alelo -α3.7 está ampliamente distribuido en el mundo, mientras que el alelo--SEA predomina en los países del sureste de Asia. El análisis de DNA del alelo--SEA mostró en 5' el sitio de ruptura en el codón 28 del pseudogén ψα2 y en 3', dentro de la secuencia Alu-Jo, localizada a 1,328 nucleótidos de la región HVR3', lo que da un segmento delecionado de 19,303 nucleótidos. Éste es el primer reporte en el que se analizan los sitios que flanquean la deleción del alelo --SEA en pacientes mexicanos y se definen con precisión los extremos 5' y 3' de la deleción.
Subject(s)
Child , Female , Humans , Male , Hemoglobin H/genetics , alpha-Thalassemia/genetics , Alleles , DNA Mutational Analysis , Mexico , Polymerase Chain ReactionABSTRACT
The aim of this study was to determine the frequency of alpha-globin gene mutations in three groups of Mexican unrelated individuals. The first two groups were normal and sickle cell trait individuals from the Costa Chica region, a place with a 12.8% frequency of HbS carriers, and the third group comprised of Mexican mestizo patients with beta-thalassemia. We searched for -alpha(3.7) and -alpha(4.2) alpha(+)-thalassemia deletion alleles, as well as the alpha alpha alpha(anti3.7) triplication through long-gap PCR. The alleles -alpha(3.7) and alpha alpha alpha(anti3.7) were found in the heterozygote state only; 19% of the normal subjects had the -alpha(3.7) allele, and 2% showed the alpha alpha alpha(anti3.7) allele. In individuals with the sickle cell trait, 17% had the -alpha(3.7) deletion, and the alpha alpha alpha(anti3.7) triplication was observed in 3% of these individuals. We revealed that 16% of the subjects with beta-thalassemia showed the -alpha(3.7) deletion and 28% the alpha alpha alpha(anti3.7) triplication. The -alpha(4.2) deletion was not detected in any individual. The frequency of the -alpha(3.7) allele was roughly the same in the three groups studied; this can be explained by the fact that the three groups have common genes from Africa and the Mediterranean, where a high prevalence of alpha(+)-thalassemia has been observed. To our knowledge, the frequency of alpha alpha alpha(anti3.7) triplication observed in the Mexican beta-thalassemia patients is the highest reported. As the -alpha(3.7) and alpha alpha alpha(anti3.7) alleles are very common in our selected populations, we believe that there is a need to investigate systematically the alpha-globin gene mutations in all hemoglobinopathies in the Mexican population.
