A novel deletion of -2.8 kb removing the entire alpha 2-globin gene observed in a Chinese patient with Hb H.

Most of recognized alpha-thalassemia mutations include deletions of one or both alpha-globin genes. Here we describe a newly detected alpha-thalassemia-2 deletion characterized by a small 2.8 kb deletion involving the a 2 globin gene. This deletion has thus far been observed in one Chinese subject with hemoglobin H disease. Its breakpoints were detected to lie between coordinates 32485 and 35381 of the alpha-globin gene cluster (NG_000006.1), with a total of 2,894 nucleotides deleted. It was designated as -alpha2.8 deletion. The proband is a compound heterozygote deletion of -SEA and -alpha2.8, and the patient displayed very mild hemoglobin H disease phenotype with hemoglobin 9.8 g/dL.

Detection of α-globin gene deletion and duplication using quantitative multiplex PCR of short fluorescent fragments.

BACKGROUND: The aim of this study was to establish a sensitive method that can detect the presence of not only the common but also the unusual or unknown α-globin gene deletions for screening of α-thalassemia. We used quantitative multiplex PCR of short fluorescent fragments (QMPSF) for the α-globin genes (HBA) to screen α-thalassemia deletions. METHODS: We set up and validated HBA-QMPSF using 50 negative and 100 positive controls of deletional α-thalassemia. To evaluate its ability to detect the presence of the common and unusual or unknown α-globin gene deletions, 579 unrelated samples were simultaneously analyzed using this assay and multiplex Gap polymerase chain reaction (Gap-PCR). The inconsistent results were further confirmed by multiplex ligation-dependent probe amplification (MLPA). RESULTS: HBA-QMPSF was capable of detecting α-globin gene deletions with an acceptable variability as shown by mean values (SD) of allele dosage for the heterozygous deleted control obtained from intra- and inter-experimental replicates [0.63 (0.01) and 0.61 (0.03)]. In 572 out of the 579 unrelated subjects, HBA-QMPSF and multiplex Gap-PCR gave consistent results. In seven cases which were finally proved to be composed of one rare deletion--Thai/-α3.7, one novel deletion--SEA/-α2.8, four αααanti3.7/αα and one αααanti4.2/αα triplications, HBA-QMPSF showed deletion or duplication in the α-globin gene while multiplex Gap-PCR failed to give the correct diagnosis. CONCLUSIONS: HBA-QMPSF is able to detect the presence of the common and unusual or unknown α-thalassemia deletions and duplications. It can be used as an initial screening test for α-thalassemia caused by HBA gene copy number alteration.