Challenges in prenatal diagnosis of beta thalassaemia: couples with normal HbA2 in one partner.

OBJECTIVES

To undertake β-genotyping in couples having normal/borderline HbA2 levels in one partner to offer the possibility of prenatal diagnosis of thalassaemia.

METHODS

A total of 967 couples were screened for β-thalassaemia. Haematological analysis was carried out on a Sysmex K-1000 analyser. The HbA2 and HbF levels were measured by High Performance Liquid Chromatography-Variant II analyser (Bio-Rad, USA). β-globin gene analysis was done by reverse dot blot hybridization, amplification refractory mutation system or DNA sequencing. Alpha globin gene triplication was determined by Multiplex PCR.

RESULTS

In 33 of 967 couples, one partner had a normal/borderline HbA2 level (1-3.5%); however a β-thalassaemia mutation could be identified in 24 of these individuals. Molecular analysis of the β-globin gene revealed the presence of the capsite +1 (A → C) [HBB: c.-50 A → C] mutation in 15 cases (60%), Poly A(T → C) [HBB: c.*110 T → C] mutation in two cases (8%), IVS 1-5 (G → C) [HBB: c. 92 + 5 (G → C)] mutation in four cases (17%) and the CD 15 (G → A) [HBB: c. 47 G → A] mutation, CD 16 (-C) [HBB: c. 51 del C] mutation and CD 30 (G → C) [HBB: c. 93 G → C] mutation in one case each (4%). Alpha gene triplication was found in five cases, while four cases remained uncharacterized.

CONCLUSIONS

β-genotyping should always be done in a couple if one partner is a β-thalassaemia carrier irrespective of the RBC indices and HbA2 levels of the other partner.