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

ABSTRACT

OBJECTIVES: To undertake ß-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 ß-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). ß-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 ß-thalassaemia mutation could be identified in 24 of these individuals. Molecular analysis of the ß-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: ß-genotyping should always be done in a couple if one partner is a ß-thalassaemia carrier irrespective of the RBC indices and HbA2 levels of the other partner.