Association of BCL11A genetic variant (rs11886868) with severity in β-thalassaemia major & sickle cell anaemia

Abstract

Background & objectives: The amount of foetal haemoglobin that persists in adulthood affects the clinical severity of haemoglobinopathies including β-thalassaemia major and sickle cell anaemia (SCA). The present study was undertaken to analyse β-thalassaemia as well as SCA patients for the single nucleotide polymorphism (SNP), rs11886868 (T/C) in BCL11A gene and to evaluate the association between this polymorphism and severity of β-thalassaemia major and SCA.

Methods: a total of 620 samples (420 β-thalassaemia major and 200 SCA cases) were analysed before blood transfusion using basic screening tests like complete blood analysis and osmotic fragility and further confirmed by high performance liquid chromatography (HPLC), amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) and reverse dot blot techniques. All patients were transfusion dependent. Patients with β-thalassaemia and SCA were classified into mild, moderate, severe according to the severity score based on Hb levels, age of onset, age at which patients received their first blood transfusion, the degree of growth retardation and splenectomy. β-thalassaemia as well as SCA patients were analysed for the SNP, rs11886868 (T/C) in BCL11A gene and association between this polymorphism and severity of β-thalassaemia major as well as SCA was evaluated.

Results: There was a significant difference in genotypic and allelic frequencies of BCL11A gene polymorphism between mild and moderate and mild and severe cases in both the groups. A significant (P<0.001) difference was observed in the mean HbF levels between the three genotypes in different severity groups. HbF levels were found to be high in CC genotype bearing individuals followed by TC and TT in β-thalassaemia major as well as SCA.

Interpretation & conclusions: This study confirms that the T/C variant (rs11886868) of the BCL11A gene causing downregulation of BCL11A gene expression in adult erythroid precursors results in the induction of HbF and ameliorates the severity of β-thalassaemia as well as SCA.

Fig 1

(a). HPLC chromatogram of a normal individual (A2- 2.1%; HbF-0.0% both A2 and HbF are in the normal range), (b) HPLC chromatogram of a β-thalassaemia carrier (A2-4.3%; HbF-0.4% A2 is high), (c) HPLC chromatogram of a sickle cell carrier (HbS- 8.8%; HbF-1.7% HbS in high range).

Fig 2

(a). HPLC chromatogram of a β-thalassaemia major (the chromatorgram is of a transfused beta thalassaemia major (A2-7.5%; HbF-3.7% both A2 and HbF are high), (b) HPLC chromatogram of a sickle cell anaemia (HbS-39.4%; HbF-10.6% both HbS and HbF are in high range), (c) HPLC chromatogram of a E-disease (A2-48.3%; hbF-3.9% A2 is too high HbF also high).

Fig 3

Gel pictures of BCL11A gene polymorphism. (a) Lanes 1, 2, 3, 5, 6, 7 and 8 represent the amplified product of BCL11A gene and lane 4 represents 100 bp ladder. (b) restriction fragment length polymorphism (RFLP) of BCL11A gene polymorphism. Lanes 1, 2 and 5 represent heterozygous condition 6, and 7 represents homozygous condition. Lane 3 represents homozygous mutant.