Prenatal diagnosis of homozygous alpha zero-thalassemia by an immunological method

Noninvasive Prenatal Diagnosis for Hemoglobin Bart's Hydrops Fetalis

Hemoglobin (Hb) Bart's hydrops fetalis, the most severe thalassemic disease, occurs from homozygosity of alpha-thalassemia 1. Deletion of all 4 alpha-globin genes (- -/- -) in this condition results in the absence of alpha-globin chains, and the physiologic dysfunction of Hb Bart's (gamma4) leads to lethality, either in utero or soon after birth. The best strategy for prevention and control of the disease is prenatal diagnosis in the mothers at risk. However, conventional prenatal diagnosis involves invasive procedures that may result in infection or abortion. In this study, a simple technique was developed to identify the presence or absence of alpha-globin chains in fetal nucleated red blood cells (NRBCs) enriched from maternal blood. Mononuclear cells including fetal NRBCs were isolated from maternal blood at 10 to 26 weeks of pregnancy by density-gradient centrifugation. Immunomagnetic separation with anti-CD71 antibody was employed to enrich fetal NRBCs, whose numbers increase with increasing gestational age. For the unaffected fetus, fetal NRBCs were detected by immunofluorescence microscopy after staining with rabbit antihuman alpha-globin antibody. In contrast, fetal red blood cells homozygous for alpha-thalassemia 1, which were identified from their size and morphology, did not stain for alpha-globin antibody. In this study, 3 affected fetuses were detected from 10 pregnancies at risk of Hb Bart's hydrops fetalis, and the results were confirmed by DNA analysis. In the remaining cases, all fetal NRBCs were positive for immunofluorescence staining. DNA analysis revealed that 2 cases were normal, 1 was heterozygous for alpha-thalassemia 2, and the other 4 cases were heterozygous for alpha-thalassemia 1.

Simple non-invasive prenatal detection of Hb Bart's disease by analysis of fetal erythrocytes in maternal blood

OBJECTIVE

To investigate a simple non-invasive technique for early detection of Hemoglobin (Hb) Bart's disease.

METHOD

Maternal blood smears from 8 known Hb Bart's pregnancies and 40 at-risk pregnancies were investigated. Maternal peripheral blood smears were stained with fluorescence-labeled monoclonal antibodies against alpha- and embryonic zeta-globin chains.

RESULTS

Fetal nonnucleated red blood cells, stained with anti-zeta but not with anti-alpha globin antibodies were found in 15 out of 16 affected pregnancies but were not detected in 23 out of 24 unaffected pregnancies.

CONCLUSION

Results showed that non-invasive immunofluorescence staining of maternal blood is a feasible approach for screening Hb Bart's disease before ultrasound manifestation in affected pregnancies.

Observations on the relationship between gamma-globin chain content and globin chain precipitation in thalassaemic erythroblasts and on the composition of erythroblastic inclusions in HbE/beta-thalassaemia

Electron microscope immunocytochemical studies were performed on the bone marrow from 2 patients each with beta-thalassaemia major and beta-thalassaemia intermedia and 4 patients with HbE/beta-thalassaemia, using the immunogold technique. Studies of sections that were reacted with mouse monoclonal antibodies against human gamma-globin chains showed the presence of large quantities of gamma-chains in several erythroblasts and marrow reticulocytes containing large amounts of precipitated globin chains. At least in these cells, substantial gamma-chains synthesis did not protect against the formation of erythroblastic inclusions, indicating that factors other than the rate of gamma-chain synthesis influence the extent of globin-chain precipitation. Studies of sections of marrow that were reacted with a rabbit polyclonal antibody against human alpha-globin chains and a mouse monoclonal antibody against human beta-globin chains showed that the erythroblastic inclusions in HbE/beta-thalassaemia did not contain detectable quantities of HbE and consisted only of precipitated alpha-globin chains. Thus, the generally milder phenotype of HbE/beta-thalassaemia cannot be attributed to co-precipitation of HbE and excess free alpha-globin chains.

Non-invasive early prenatal molecular diagnosis using retrieved transcervical trophoblast cells

Fetal DNA was recovered from 17 of 39 (44%) transcervical cell (TCC) samples obtained between 7 and 9 weeks of gestation by endocervical canal flushing. Trophoblast retrieval was adequate for polymerase chain reaction (PCR) amplification of Y chromosome-specific DNA sequences and detection of paternal-specific microsatellite alleles. The fetal sex predicted by PCR in TCCs was confirmed in all cases by karyotype analysis of chorionic villi at 10 weeks of gestation. The absence of the disease-associated paternal alleles in TCC samples from two pregnancies at risk for spinal muscular atrophy and myotonic dystrophy predicted unaffected fetuses in agreement with subsequent results on chorionic villi and newborns' leukocytes. A trisomy 21 fetus was diagnosed in TCCs using fluorescent in situ hybridization (FISH) and semi-quantitative PCR analysis of superoxide dismutase-1 (SOD 1). Present experience indicates that TCC sampling is a promising technique for early prenatal monitoring of Mendelian disorders and chromosome aneuploidy.