ABSTRACT
Introduction: We report the first successful preimplantation genetic diagnosis (PGD) for Hb Bart’s hydrops fetalis in Singapore, involving both fresh and frozen embryo replacement cycles. Clinical Picture: Two couples who were carriers of the Southeast Asian type double gene deletion (--SEA deletion carriers) requested for PGD. Couple A had 2 previous affected pregnancies, while couple B have a child of unknown genotypic status. Treatment: One PGD cycle was performed for each couple. The --SEA deletion was detected using a gap-PCR strategy. Couple A had 1 fresh-embryo replacement cycle while couple B underwent 2 frozen-embryo replacement cycles. Outcome: Couple A achieved a twin pregnancy. Second trimester complications resulted in premature delivery, where 1 baby girl survived. Couple B achieved a singleton pregnancy resulting in delivery of a healthy baby boy. Genotype analysis of all babies confirmed the PGD results consistent with clinically unaffected status. Conclusions: We have successfully performed PGD to avoid Hb Bart’s hydrops fetalis syndrome.
Alpha-thalassaemia is one of the most common genetic disorders worldwide. It results from absent or reduced production of a-globin chains caused by mutations in the a-globin gene cluster. The a-thalassaemia mutations usually involve deletions of one (-a) or both (–) a-globin genes, and are prevalent within Southeast Asia. In Singapore, the carrier frequency for a-thalassaemia mutations is about 6.4% in the Chinese, 4.8% in Malays, and 5.2% in Indians.1 Couples who are both heterozygous for an a-globin double gene deletion (a0 -thalassaemia) have a 25% risk of conceiving a baby with Hb Bart’s hydrops fetalis syndrome resulting from homozygous a0 -thalassaemia, who will either die in utero late in gestation or soon after birth. This syndrome is associated with an increased risk of maternal complications including hypertension, eclampsia and antepartum haemorrhage.2 Therefore, genetic counselling and prenatal diagnosis are important for at-risk couples who wish to avoid having an affected baby. However, the positive prenatal diagnosis of an affected foetus can be emotionally painful, as parents have to grapple with the difficult decision of pregnancy termination.
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