Tan JAMA1, Wee YC1, Tan KL1, Wong YC1, Chow WPT1, Yap SF3
1. Department of Allied Health Sciences. Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur
2. Department of Obstetrics and Gynaecology, Faculty of Medicine, University of Malaya
3. Department of Pathology, Faculty of Medicine, University of Malaya
Correspondence: JAMA Tan; E-mail:
CITATION: Tan JAMA, Wee YC, Tan KL, Wong YC, Chow WPT, Yap SF. Antenatal diagnosis for alpha-thalassaemia in Malaysia-a four year review from 1996-2000. International Medical Research Journal. 2000;4(2):73–7.
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. Antenatal diagnosis using CV DNA is encouraged as CY sampling is carried out at 10 weeks gestation and termination of a pregnancy at this stage is safer and less traumatic for the mother. DNA amplification of the 136 bp ψα-α2-globin gene region together with amplification of the 660bp --SEA fragment offers a rapid, specific and affordable confirmatory test in the antenatal diagnosis of Bart's hydrops foetalis in Malaysia.
KEYWORDS: α-thalassaemia, antenatal diagnosis, Bart's hydrops foetalis, DNA amplification
