Prenatal diagnosis for beta-thalassemia syndromes using HRP-labeled oligonucleotide probes at Siriraj Hospital.

Characterization of the molecular defect of beta-thalassemia in Thais has enabled us to establish prenatal diagnosis for homozygous beta-thalassemia and beta-thalassemia/Hb E. The nature of the beta-thalassemia mutation of each high risk couple or of the previous affected child was firstly identified after counseling. Detection of beta-thalassemia mutations was performed by dot-blot hybridization of the amplified DNA with a set of HRP-labeled ASO-probes specific for the common mutations. If the mutation could be characterized, prenatal diagnosis (PND) would be performed by using DNA extracted either from the chorionic villi (CVS) or amniotic fluid fibroblast in the first trimester of pregnancy or from fetal blood in the second trimester. DNA analysis was carried out in 23 couples at risk of having homozygous beta-thalassemia and 88 couples at risk for beta-thalassemia/Hb E. However, PND was performed by this technique in 22 pregnancies from 21 couples at risk of having homozygous beta-thalassemia children and 86 pregnancies from 71 couples at risk for beta-thalassemia/Hb E; 9 couples underwent more than one prenatal diagnosis. The results showed that, although there are more than 20 beta-thalassemia mutations in the Thai population, PND by DNA analysis could be carried out in more than 95% of the risk couples by using beta(E) and 10 different HRP-labeled ASO probes. This technique was simple, economic and avoided the use of radioactive isotope.

Prenatal diagnosis of thalassemia and hemoglobinopathies in Thailand: experience from 100 pregnancies.

In this review, we describe a simple strategy to detect the three severe thalassemic diseases commonly found in Thailand. Hb Bart's hydrops fetalis can be detected unambiguously by ultrasonography at 18-20 weeks of gestation or detected early in the first trimester by the gene amplification technique. Prenatal diagnosis for homozygous beta-thalassemia is better performed in the second trimester by in vitro protein synthesis. This is because the molecular defects of some beta-thalassemias are still unknown and homozygosity of the same mutation is low. In contrast, beta-thalassemia/Hb E is easily detected, in the first trimester, by direct visualization on electrophoresis or by dot blot analysis of enzymatically amplified DNA with a set of nonradioactively labeled oligonucleotide probes complementary to the most common mutations. We also found that the beta/gamma synthesis ratio in homozygous Hb E is similar to that of beta-thalassemia/Hb E and DNA analysis is the only method to distinguish these two conditions in the couple at risk of having either beta-thalassemia/Hb E or asymptomatic homozygous Hb E. In 100 pregnancies studied, the diagnoses were achieved in 96 pregnancies. Complications leading to fetal loss were found in 3 pregnancies: one woman developed amnionitis after fetal blood sampling; one had amniotic fluid leakage after the biopsy, and the third, carrying a normal fetus, aborted 10 days after fetal blood sampling with urinary tract infection and high fever. However, these figures are compatible with other reports and the risks are significantly lower than that of thalassemic disease the fetus is facing. One case of beta-thalassemia/Hb E was incorrectly diagnosed prenatally as being Hb E trait. In twenty-five pregnancies (25%) prenatally diagnosed to carry affected fetuses it was decided to have abortion. This study shows the feasibility of prenatal diagnosis for thalassemic diseases in Thailand which, in addition to screening and genetic counseling, can support prevention and control programs for thalassemia.

Percutaneous umbilical cord blood sampling.

Percutaneous umbilical cord blood sampling is a newer, safer, and more convenient technique and can be performed in the second and third trimester of pregnancy by direct puncture of the umbilical vein near its placental insertion, using a needle guided by ultrasound. Between 2-4 ml of pure fetal blood were obtained from 10 pregnancies at between 19 and 39 weeks' gestation. This new procedure offers access to the fetal circulation for diagnosis and therapeutic purposes.