The Risk of α-Thalassaemia in Offspring of β-Thalassaemia Carriers in Hong Kong

Couples in whom one is heterozygous for α‐thalassaemia‐1 and the other is heterozygous for β‐thalassaemia are assumed not to be at risk of having offspring with homozygous α‐thalassaemia‐1 or homozygous β‐thalassaemia. We retrospectively reviewed the genetic outcome of 189 pregnancies of 178 couples in whom the partners were diagnosed to be discordant heterozygotes of α‐thalassaemia and β‐thalassaemia on haematological tests. ζ gene mapping was performed on 158 β‐thalassaemia carriers to diagnose the presence of co‐existing α‐thalassaemia‐1. Eleven patients (7 per cent) were found to be compound α‐ and β‐thalassaemia heterozygotes. They accounted for 16 pregnancies, of which five were diagnosed to be affected by homozygous α‐thalassaemia‐1. Our results show that couples presumed to be discordant heterozygotes of α‐ and β‐thalassaemia on haematological testing are at risk of having offspring with homozygous α‐thalassaemia‐1 if the ζ gene mapping of the heterozygous β‐thalassaemia partner shows co‐inheritance of α‐thalassaemia‐1. Prenatal diagnosis of homozygous α‐thalassaemia‐1 should be performed on these at‐risk pregnancies. © John Wiley & Sons, Ltd.