Free fetal DNA in maternal plasma in anembryonic pregnancies: confirmation that the origin is the trophoblast

OBJECTIVE

To test the hypothesis that free fetal DNA (ffDNA) circulating in maternal plasma originates mainly from the placenta we studied ffDNA levels in anembryonic pregnancies.

METHODS

Maternal blood samples were collected from 15 normal first-trimester pregnancies in which fetal sex was subsequently determined and nine patients with a diagnosis of anembryonic gestation (AG). The Y chromosome DYS14 gene was quantified by real-time quantitative PCR (RT-PCR) for the determination of fetal sex in both plasma and chorionic tissue samples. Fetal sex in chorionic tissue samples was also determined using quantitative fluorescence PCR (QF-PCR).

RESULTS

The correct sex result was obtained from maternal plasma in all. Four AG pregnancies were female (DYS14 negative) results. In five of the AG cases, the chorionic tissue was found to be male (by both QF-PCR and RT-PCR which agreed) and positive male signal was found in maternal plasma by RT-PCR. There was no statistical difference between median free fetal DNA concentration in plasma between the AG male cases (148.3 GE/mL) and controls (145.8 GE/mL).

CONCLUSION

Since ffDNA levels are normal in pregnancies without a fetus, the data support the hypothesis that the trophoblastic cells are the major source ffDNA in maternal plasma.

Rh null phenotypes are not due to a gross deletion and can occur on different Rh genetic backgrounds

Alu element-primed PCR was performed on genomic clones containing human RH blood group genes. When used as a probe, the Alu PCR product detected a restriction fragment-length polymorphism which is in complete linkage disequilibrium with the Rh C/c serological polymorphism, irrespective of the Rh D or E serological type it is coupled with. This provides the opportunity to type individuals for their RH C gene directly at the DNA level. RFLP analysis of two individuals with the amorph Rh null phenotype revealed that in one case this phenotype occurred on an RH C background, whereas in the other it was on an RH c background. Taken together these results indicate that the Rh C/c polymorphism has arisen only once, but that the amorph Rh null phenotype, although exceedingly rare, is the result of at least two independent mutations.

Monoclonal antibodies that recognize different membrane proteins that are deficient in Rhnull human erythrocytes. One group of antibodies reacts with a variety of cells and tissues whereas the other group is erythroid-specific

1. Rhnull human erythrocytes lack all of the antigens of the Rh and LW blood group systems and have abnormal shape and an increased osmotic fragility. In this paper two murine monoclonal antibodies raised against intact human erythrocytes were used to investigate further the abnormalities in these cells. BRIC 125 reacts weakly with Rhnull erythrocytes and BRIC 69 does not react at all. The results showed that BRIC 125 reacts with a component of Mr 47,000-52,000 which has a substantial content of N-glycans. In contrast, BRIC 69 reacted with a band of Mr 31,000 together with a very diffuse band of Mr 35,000-52,000. Treatment of BRIC 69 immunoprecipitates with endoglycosidase F/peptidyl-N-glycosidase F resulted in the loss of both BRIC 69 reactive components and the appearance of a new band of Mr similar to that of the Rh(D) polypeptide. 2. BRIC 125 had a broad reactivity with cells in peripheral blood, whereas the reactivity of BRIC 69 was confined to erythrocytes. BRIC 125, but not BRIC 69, reacted with human kidney tissue and bound to endothelium in peritubular capillaries, arteries and veins as well as the epithelial tissue of distal tubules. BRIC 125 stained haemopoietic cells, foetal hepatocytes and megakaryocytes in foetal liver and sinusoidal cells, hepatocytes and portal tracts in adult liver. In contrast, BRIC 69 reactivity was confined to haemopoietic cells in foetal liver. The BRIC 125 epitope has a wide tissue distribution, suggesting the occurrence of a related group of polypeptides which have a general functional role on cell surfaces. 3. Rhnull erythrocytes are deficient in at least four different membrane polypeptides.