The risk of α-thalassaemia in offspring of β-thalassaemia carriers in Hong Kong

Abstract

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.