Accurate Prenatal Diagnosis of Hb Bart’s Hydrops Fetalis in Daily Practice with a Double-Check PCR System

Abstract

Hemoglobin (Hb) Bart’s hydrops fetalis is a fatal condition associated with homozygous α⁰-thalassemia. Prenatal diagnosis of the disease is usually done by gap-PCR; however, misdiagnosis can occur with allelic dropout. Diagnosis using more than one method is preferred. We describe a double-check PCR assay for accurate prenatal diagnosis. The study was conducted on 64 fetuses at risk of homozygous α⁰-thalassemia encountered at our routine thalassemia diagnosis laboratory. Chorionic villus sample (CVS), amniotic fluid or fetal blood specimens were obtained from pregnant women at risk and analyzed by two PCR methods. In the first method, the SEA α⁰-thalassemia deletion of parents and fetuses were determined by gap-PCR routinely run in our laboratory. In another method, two specific fragments located 5′ to the ζ₂ gene (XbaI fragment) and the α₂-globin gene (RsaI fragment) together with the gap-PCR fragment were multiply co-amplified to determine the presence or absence of normal and α⁰-thalassemia alleles. The molecular diagnosis of α⁰-thalassemia was possible in all 64 fetuses using the two PCR approaches. The final diagnoses included 13 normal, 29 unaffected heterozygote and 22 homozygote α⁰-thalassemia fetuses.The two PCR assays disclosed no discordant result in the diagnosis of the Hb Bart’s hydrops fetalis caused by α⁰-thalassemia.The combined PCR assay for gap-PCR, ζ₂ XbaI and α₂ RsaI fragments, described here, is simple, accurate and applicable in the prenatal diagnosis of Hb Bart’s hydrops fetalis in a routine setting.