Co-inheritance of alpha-and beta-thalassemia in Khuzestan Province, Iran

beta-thalassemia is one of the most frequent hemoglobinopathies and single gene disorders in Iran. About 13 beta globin mutations encompass 70-90% of mutations spectrum in Iran, the rest are rare or unknown. People who do not produce enough alpha globin protein chains have alpha-thalassemia. This is commonly found in Africa, the Middle East, India, Southeast Asia, southern China, and occasionally the Mediterranean region. There are normally four alpha globin genes, two on each chromosome 16. Individuals who have one or two abnormal alpha globin genes have alpha-thalassemia trait. The aim of this study was to detect alpha-thalassemia in beta-thalassemia carriers during prenatal screening.

A total of 158 couples were diagnosed to be discordant alpha- and beta-thalassemia carriers. We used the routine screening for thalassemia which includes full blood counts and indices, hemoglobin electrophoresis and measurement of Hb A(2) level. The standard diagnostic marker for beta-thalassemia is elevation of the Hb A(2) level (>3 x 5%). Low mean corpuscular volume (MCV) and mean cell hemoglobin (MCH) with a normal Hb A(2) indicate an alpha-thalassemia carrier. Staining for HbH inclusion bodies is also carried out as part of the screening for alpha thalassemia. The 59 and 39 ends of the breakpoint regions of the -alpha(4 x 2) allele and the normal homologous segments were sequenced in selected individuals.

Of the 158 beta-thalassemia partners, seven (4 x 4%) were found to have co-inheritance of alpha(+)-thalassemia, and three (1 x 9%) found to have co-inheritance of alpha(0)-thalassemia. Two pregnancies affected with Hb Bart's hydrops fetalis were terminated in the 158 couples. A sequence haplotype was found in all of the five Iranian -alpha(4 x 2) thalassaemia alleles studied. Based on these findings, a novel polymerase chain reaction (PCR)/denaturing high performance liquid chromatography (DHPLC) assay was developed for rapid genotyping of the -alpha(4 x 2) allele instead of traditional Southern blotting or Gap-PCR. This method involves amplification of the alpha globin target sequence encompassing these four polymorphic sites, followed by a partially denaturing HPLC analysis using the transgenomic WAVE DNA fragment analysis system. The major genotypes (-alpha(4 x 2)/alpha alpha, -alpha(4 x 2)/--(MED), -alpha(3 x 7)/alpha alpha, -alpha(3 x 7)/-alpha(3 x 7), alpha alpha/--(MED) and alpha alpha/alpha alpha) could be distinguished through the characteristic chromatograms generated by the WAVE system.

The results showed that molecular analysis must be used for accurate diagnosis of double heterozygotes in couples presumed to be discordant for alpha- and beta-thalassemia on hematologic testing. The accuracy of this technique was evaluated blindly, and the results were 100% (40 of 40) concordant with the genotypes previously characterized by Southern blotting or Gap-PCR.