Detection and characterisation of β-globin gene cluster deletions in Chinese using multiplex ligationdependent probe amplification

Background: Deletions in the β-globin cluster causing thalassaemia and hereditary persistence of fetal haemoglobin (HPFH) are uncommon and difficult to detect. Data in Chinese are very scarce. Aims: To use a recently available technique to investigate the frequencies and nature of β-globin cluster deletions in Chinese. Methods: 106 subjects with phenotypes of thalassaemia or HPFH and suspected to have deletions in the β-globin cluster were studied. A commercially available kit employing multiplex ligation-dependent probe amplification (MLPA) was used to screen for deletions. Gap PCR and direct nucleotide sequencing were used to characterise deletions detected. Results: 17 deletions in the β-globin cluster were found in 17 patients: 8 of Chinese (Aγδβ)0 thalassaemia, 7 of Southeast Asian (Vietnamese) deletion and 2 of Thai (Aγδβ) 0 thalassaemia. The only type of deletion detected in δβ-thalassaemia was Chinese (Aγδβ) 0 thalassaemia. The deletional form of HPFH was rarely seen in only 1 case of Thai (Aγδβ)0 thalassaemia. Deletions presenting as β-thalassaemia trait and raised HbF were all of the Southeast Asian (Vietnamese) deletion type. When these deletions were co-inherited with classical β-thalassaemia mutations in compound heterozygous states, the phenotypes could be very variable. Conclusions: In the Chinese population, there are only relatively few types of deletions seen in the β-globin cluster. MLPA is a fast and effective way of screening for these deletions. Characterisation of these deletions allows the development of simpler and more specific PCR-based tests for routine diagnostic use. Accurate prediction of phenotype is not always feasible. The molecular defects in many cases of HPFH still await discovery.published_or_final_versio

A novel beta-delta globin gene fusion, anti-Lepore Hong Kong, leads to overexpression of delta globin chain and a mild thalassaemia intermedia phenotype when co-inherited with β0-thalassaemia

Anti-Lepore haemoglobins (Hb) are rare βδ fusion variants that arise from non-homologous crossover during meiosis, resulting in a δ-βδ-β configuration. A novel anti-Lepore mutation (anti-Lepore Hong Kong) was found in two Chinese families with raised Hb A 2. Direct sequencing revealed a crossover within a 54-bp region spanning the junction of cap site (CAP) and exon 1, which predicted the production of normal δ-globin. Determination of α/β-mRNA ratios by quantitative real-time polymerase chain reaction demonstrated downregulation of the β gene in cis due to the interposed βδ fusion gene. Although heterozygotes have normal red cell indices and are clinically silent, compound heterozygotes with β0 mutation in trans produce a mild thalassaemia intermedia phenotype with a markedly raised Hb A2 level that may mimic clinically mild Hb E-β+-thalassaemia. Awareness of the presence of anti-Lepore Hong Kong will help to resolve diagnostic problems in regions with significant prevalence of globin disorders. © 2007 The Authors.link_to_OA_fulltex

A novel beta-delta globin gene fusion leads to over-expression of delta globin chain and a mild thalassemia intermedia phenotype when co-inherited with beta-zero thalassemia

Anti-Lepore hemoglobins are rare βδ fusion variants that arise from nonhomologous crossover during meiosis, resulting in a δ-βδ-β configuration in the β globin cluster on the short arm of chromosome 11. No such variant has previously been reported in Chinese. We studied 2 unrelated Chinese families with anti-Lepore due to a novel βδ fusion. A moderate increase of Hb A2 to between 16.8 and 19.2% of total Hb was seen in 4 clinically and hematologically normal carriers, while in 1 patient with concurrent β thalassemia allele and mild thalassemia intermedia phenotype, the Hb A2 was markedly raised to 42.2%. Potential βδ fusion gene was amplified using PCR with primer 5′ to β globin gene Cap site and 3′ to δ globin gene poly A region in these 5 subjects. Direct sequencing of the PCR products revealed a crossover between the β and δ globin gene within a 54 bp region spanning the junction of CAP and exon 1 in all 5 subjects. Active transcription of this novel βδ fusion gene was studied in 2 subjects (1 normal carrier and the patient with thalassemia intermedia). Using primer pair 5′ to β globin gene Cap site and at the 3′ end of δ globin gene exon 3, a 655 bp PCR product was obtained from cDNA in both subjects. Direct sequencing confirmed the presence of a βδ fusion mRNA. The predicted protein product of this fusion gene was identical to δ globin, since only the 5′ untranslated region was β specific. Determination of α/β mRNA ratios by quantitative real-time PCR was performed in 2 normal carriers (ratio 3.28 and 3.95) and the patient with thalassemia intermedia (ratio 25.59). These were compared with ratios ± standard deviation from 20 normal controls (1.92±0.55), 5 unrelated patients with β thalassaemia minor (17.23±5.38) and 3 unrelated patients with β thalassemia major (139.21±39.50). Mild down-regulation of the β gene in cis due to this interposed βδ fusion gene was demonstrated. Although heterozygotes of this novel anti-Lepore Hb had normal red cell indices and were clinically silent, compound heterozygotes with β0 mutation in trans produced a mild thalassemia intermedia phenotype with a markedly raised Hb A2 level that might mimic clinically mild Hb E-β+ thalassemia. Awareness of this new anti-Lepore Hb will help to resolve diagnostic problems in regions with significant prevalence of globin disorders. © 2006, The American Society of Hematolog