Detection and characterisation of [beta]-globin gene cluster deletions in Chinese using multiplex ligation-dependent 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 (A [GAMMA]δβ)0 thalassaemia, 7 of Southeast Asian (Vietnamese) deletion and 2 of Thai (A [GAMMA]δβ)0 thalassaemia. The only type of deletion detected in δβ-thalassaemia was Chinese (A [GAMMA]δβ)0 thalassaemia. The deletional form of HPFH was rarely seen in only 1 case of Thai (A [GAMMA]δβ)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.