Antenatal diagnosis for alpha-thalassaemia in Malaysia - a four year review from 1996 - 2000

Abstract

Antenatal diagnosis for homozygous α⁰-thalassaemia (Bart's hydrops foetalis) is currently carried out by DNA amplification of two sequences along the α-gene complex- a 136 bp ψα-α2-globin gene sequence and a 660 bp--^SEAdeletion-specific fragment. The fatal condition Bart's hydrops foetahs with a 20 kb deletion of both α-genes does not amplify the 136 bp normal bp ψα-α2-globin gene sequence but amplifies only the 660 bp- ^SEA fragment. lndividuals who are α⁰-thalassaemia-carriers (αα/--^SEA) amplify both the 136 bp and 660 bp fragments. whereas normal individuals (αα/αα) only produce the 136 bp fragment. We retrospectively reviewed the results of antenatal screening for α-thalassaemia in the University of Malaya Medical Centre, over a four-year period from October 1996 October 2000. Antenatal diagnosis was carried out using foetal blood and chorionic villi (CV) samples. A total of 95 pregnancies from 77 Chinese families at risk for Bart's hydrops foetalis were screened. Of these 95 antenatal diagnoses, 16.8 % did not carry the --^SEA deletion. 35.8 % were α-thalassaemia carriers with the SEA deletion ( --^SEA) and 47.4 % were diagnosed with Bart 's hydrops foetalis (--^SEA/ --^SEA). In addition, foetuses in 23.2 % (22/95) of the pregnancies already showed hydropic features when referred for antenatal diagnosis, and 95.5 % (21 /22) of these pregnancies were confirmed to be Bart's hydrops foetalis. Antenatal diagnosis using CV samples increased from 33.3% (5/15) in 1997 to 88.9 % (24/27) in 2000 while diagnosis using foetal blood decreased dramatically over the same period.