THE RISK OF ALPHA-THALASSEMIA IN OFFSPRING OF BETA-THALASSEMIA CARRIERS IN HONG-KONG

Couples in whom one is heterozygous for alpha-thalassaemia-1 and the o ther is heterozygous for beta-thalassaemia are assumed not to be at ri sk of having offspring with homozygous alpha-thalassaemia-1 or homozyg ous beta-thalassaemia. We retrospectively reviewed the genetic outcome of 189 pregnancies of 178 couples in whom the partners were diagnosed to be discordant heterozygotes of alpha-thalassaemia and beta-thalass aemia on haematological tests. zeta gene mapping was performed on 158 beta-thalassaemia carriers to diagnose the presence of co-existing alp ha-thalassaemia-1. Eleven patients (7 per cent) were found to be compo und alpha- and beta-thalassaemia heterozygotes. They accounted for 16 pregnancies, of which five were diagnosed to be affected by homozygous alpha-thalassaemia-1. Our results show that couples presumed to be di scordant heterozygotes of alpha- and beta-thalassaemia on haematologic al testing are at risk of having offspring with homozygous alpha-thala ssaemia-1 if the zeta gene mapping of the heterozygous beta-thalassaem ia partner shows co-inheritance of alpha-thalassaemia-1. Prenatal diag nosis of homozygous alpha-thalassaemia-1 should be performed on these at-risk pregnancies. (C) 1997 by John Wiley & Sons, Ltd.