An investigation into the effects of alpha thalassaemia on haemoglobin E level by high performance liquid chromatography in heterogeneous haemoglobin E carrier in Hong Kong

Abstract

BACKGROUND: Thalassaemia is an inherited blood disorder characterised by reduced α- and β-globin chain production and imbalance due to the defects of globin alleles. It has a high prevalence among the Chinese population in the Southeast Asia. The severity of subclasses, α- and β-thalassaemia, depends on the number of affected globin alleles and can be caused by deletional and/or non-deletional mutation(s). Haemoglobin E (HbE) is mutated haemoglobin with a single point mutation in β-globin chain, which can be detected as variant haemoglobin in high performance liquid chromatography (HPLC) and densitometry. In rare patients with concomitant heterogeneous HbE and α-thalassaemia, there is interaction between HbE and α-thalassaemia leading to the changes in the pattern in HPLC and densitometry.

OBJECTIVES: The aim is to investigate the effects of α-thalassaemia on HbE in heterogeneous HbE carrier in Hong Kong and/or the Chinese population by studying HbE level by HPLC and densitometry in subjects with HbE with concomitant α-thalassaemia and comparing that with a typical HbE without thalassaemia.

DESIGN: Known samples, n = 58, that recently diagnosed with heterogeneous HbE by elevated HbE level up to ~30% in HPLC were selected for further phenotypic and genotypic analysis, including complete blood count, HbH inclusion bodies screening, haemoglobin electrophoresis for densitometry, α-globin multiplex gap-polymerase chain reaction (PCR) and α-amplification refractory mutation system-PCR, for the determination of the presence of HbE with concomitant α-thalassaemia. Known samples, n = 126, that clinically diagnosed with heterogeneous HbE by HPLC were retrospectively collected from database for selecting patients of interest with HbE with concomitant α-thalassaemia. (n = 184)

RESULTS: 27 out of 184 (14.67%) known heterogeneous HbE patients were suggested to be and/or indicated with HbE with concomitant α-thalassaemia, with the HbA2 + HbE level in HPLC ranging from 17.3% - 25.7%.

CONCLUSION: Interactions were found between heterogeneous HbE and α-thalassaemia, resulting in a drop of HbA2 + HbE level in HPLC and densitometry, when comparing to a typical HbE without thalassaemia. A cut-off line was set for heterogeneous HbE carrier in Hong Kong and/or the Chinese population with <26.0% HbE level by HPLC, is suggested to have a relatively high possibility to be diagnosed with HbE with concomitant α-thalassaemia, leading to a complex haemoglobinopathy.