OBJECTIVETo develop a simple, rapid, accurate, and cost-effective single-0tube multiplex polymerase chain reaction (PCR) assay, which could be used for molecular screening and prenatal diagnosis, for detection of three commonest deletional alpha-thalassemias (-- (SEA), -alpha (3.7) and -alpha (4.2)) in Chinese population.

METHODSFour groups of primers were designed on the basis of gap-PCR, and the PCR reaction condition was optimized systematically with the purpose of amplifying effectively specific DNA fragments that are indicative of the respective genotypes of these three deletional alpha thalassemias. In addition, a pair of primers was designed to amplify LIS1 3' untranslated region (UTR) fragment for use as a separate control for amplification running. A total of 72 blood and prenatal archival DNA samples with various known alpha thalassemia genes or normal alpha globin gene sequence that had been confirmed by Southern blotting analysis or DNA sequencing were collected to test the specificity of this assay by blind analysis. In addition, DNA samples from nine couples at high risk of alpha thalassemia were also analyzed to evaluate the reliability of this technique in prenatal implementation.

RESULTSHomozygote, heterozygote and double heterozygote of the three commonest deletional alpha thalassemias were well detected simultaneously by this established method. For normal allele, a 2.4 kb amplified band as a systematic control and an alpha (2) gene-specific amplicon of 1.8 kb were produced. Besides the two amplified fragments of normal allele, it was found that a 1.3 kb, a 2.0 kb or a 1.6 kb amplified band could be simultaneously shown for representing --(SEA), -alpha (3.7) and -alpha (4.2) alleles, respectively, in the heterozygous states. In a blind test, this technique accurately detected 100% of the DNA samples previously characterized by Southern blotting or DNA sequencing, and it was successfully applied to prenatal diagnosis of alpha thalassemia in nine at-risk families.

CONCLUSIONThe single-tube multiplex PCR protocol presented in this study is easy-to-handle, rapid, reliable and is cost-effective for detecting --(SEA), -alpha (3.7) and -alpha (4.2) chromosomes, and it is suitable for large-scale population screening and for rapid molecular genotyping in clinics.