Apoptosis in fetal nucleated erythrocytes circulating in maternal blood

Prenatal screening of single-gene disorders from maternal blood

Fetal cells and cell-free fetal DNA can be found circulating in maternal blood. Fetal cells recovered from maternal blood provide the only source of pure fetal DNA for noninvasive prenatal DNA diagnosis. Fetal nucleated erythrocytes (NRBCs) are considered the most suitable maternally-circulating fetal cells for this purpose, because they are not commonly found in the peripheral blood of healthy adults and are most abundant in the fetus during early gestation. Because fetal cells in maternal blood are extremely rare, a definitive separation method has not yet been established. Fetal NRBCs can be enriched from maternal blood via fluorescence- or magnetic-activated cell sorting, density gradients, immuno-magnetic beads or micromanipulation. Fetal cells are identified by Giemsa staining, hybridization with Y-chromosome specific probes, PCR-detection of a specific paternal allele, or immunostaining for fetal cell antigens. Amplification of fetal DNA sequences by primer extension preamplification and PCR has allowed prenatal screening for Duchenne muscular dystrophy and the fetal RhD blood type. Sequence-specific hybridization has been used to detect sickle cell anemia and beta-thalassemia prenatally in heterozygous carriers of these disorders. The use of cell-free fetal DNA in maternal plasma for the diagnosis of single-gene disorders is limited to disorders caused by a paternally inherited gene or a mutation that can be distinguished from the maternally inherited counterpart. At present, fetal gender can be determined from maternal plasma. When a pregnant woman is a heterzygous carrier of an X-linked disorder, the determination of fetal gender is clinically very informative for first-step screening to avoid invasive amniocentesis. The non-invasive prenatal diagnosis of genetic disorders should be applied to pregnant women with a definite risk for a specific single-gene disorder.

Developments in laboratory techniques for prenatal diagnosis

Ongoing trends in prenatal diagnosis aim at early, rapid, and ideally noninvasive diagnosis as well as at the improvement of risk-screening for aneuploidy. Interphase-fluorescence in situ hybridization and quantitative fluorescence polymerase chain reaction are efficient tools for the rapid exclusion of selected aneuploidies in addition to the established direct preparation of chromosomes from chorionic villi. Interphase fluorescence in situ hybridization has also made possible the diagnosis of selected chromosome abnormalities in single cells (e.g. in preimplantation genetic diagnosis) or noninvasive diagnosis. More complex multicolor fluorescence in situ hybridization approaches are currently being evaluated. Single cell polymerase chain reaction is the key technique for the molecular diagnosis of a growing number of monogenic conditions before implantation or, still more experimental, in fetal cells retrieved from the maternal circulation. New sources for noninvasive diagnosis came into play such as fetal DNA or cell nuclei in maternal plasma. The combination of biochemical parameters in the maternal serum, namely free beta-human chorionic gonadotropin with pregnancy associated plasma protein A and sonographic markers, has already dramatically increased the sensitivity of risk screening in the first trimester of pregnancy.

Testing normality of fetal DNA concentration in maternal plasma at 10-12 completed weeks' gestation: a preliminary approach to a new marker for genetic screening

OBJECTIVES

To test the distribution of fetal DNA in maternal plasma expressed as gen/eq in a population of normal pregnancies.

METHODS

Peripheral blood samples were obtained from 63 women (85% > or =35 years of age at delivery) bearing a euploid male fetus. Each patient underwent chorionic villus sampling (CVS) for karyotype analysis and/or beta thalassemia screening. Ultrasound scanning was used to determine gestational age. At 10-12 weeks' gestation, a peripheral blood sample was collected followed by CVS. To detect the Y chromosome specific sequences (SRY) quantitative polymerase chain reaction (PCR) analysis was used. Normal distribution of the data was tested by means of the Kolmogorov-Smirnov (KS) test. A Symmetry test (reliability p>0.05) was used to evaluate the reliability of the median.

RESULTS

Only after natural logarithmic transformation did the data display a normal distribution. The median value of fetal DNA was 23.3 gen/eq (range 2.08-195), interquartile range 18.57-45.4. A Pearson test showed a significant correlation between gestational age and fetal DNA concentration (r=0.25, p=0.045).

CONCLUSION

The present finding is a preliminary step towards a possible integration of fetal DNA with other variables (biochemical and/or ultrasound). It may serve to improve the discrimination of the screening for genetic diseases in the first trimester. Because of the relatively high dispersion, adjustments for possible covariates would appear to be necessary in further studies.

Application of fetal DNA in maternal plasma for noninvasive prenatal diagnosis

Prenatal diagnosis of fetal genetic conditions is a standard part of modern obstetric care. Many of the current methods rely on invasive methods and are associated with an inherent risk of fetal loss. Consequently, there has been a long-term goal for development of noninvasive prenatal diagnostic methods. In 1997, the presence of fetal DNA in maternal plasma was first discovered through the detection of Y-chromosome-specific sequences in the plasma of women conceived with male fetuses. This discovery has opened up new possibilities in the development of noninvasive prenatal diagnostic methods through a source of fetal genetic material that could be conveniently accessible simply through the collection of a maternal peripheral blood sample. To date, there have been numerous reported applications, including fetal RhD genotyping, prenatal diagnosis of sex-linked disorders, paternally inherited genetic diseases and some pregnancy-associated conditions, including preeclampsia. More recently, there have been significant new developments with expanding number of potential applications.

Circulating fetal DNA in maternal plasma

BACKGROUND

The existence of high concentrations of circulating fetal DNA in maternal plasma may enable non-invasive prenatal diagnosis. There are many applications of fetal DNA in maternal plasma for clinical diagnosis.

CONCLUSIONS

We expect fetal DNA in material plasma will be incorporated into past of the prenatal investigation of pregnant women in the near future.

Use of annexin V antibody to identify apoptotic cells during pregnancy

In a previous study, we demonstrated that apoptosis increased according to gestational age, accounting partly for the presence of free fetal DNA in maternal plasma and serum. Using simultaneous TUNEL assay and FISH analysis, we identified the fetal origin of part of the apoptotic cell population, but very few TUNEL-positive cells showed hybridization signals since they were in a late apoptosis stage and nuclei were destroyed. In the present study, the apoptotic cell population was identified immunocytochemically using Annexin V, a marker of cells in an early stage of apoptosis. The mean apoptosis rate in mononuclear cells isolated from the peripheral blood of 20 pregnant women in the 16th to 19th week of pregnancy with Annexin V was 6.8 +/- 0.5% (range: 4.2-8.1%) compared to 6.14 +/- 0.5% (range: 3.7-6.9%) obtained with ethidium bromide staining. FISH using X and Y chromosome-specific probes was applied in 11 cases known to be carrying male fetuses. Eighty percent of Annexin V+ cells showed hybridization signals, while the proportion of apoptotic cells showing X/Y signals was 7.8% (range: 5-12%). Although our results are still preliminary, it seems that use of Annexin V antibody to detect the apoptotic cell population improves FISH analysis and allows a more accurate estimate of the proportion of fetal cells among the apoptotic cell population.

Diagnosis of Trisomy 21 in Fetal Nucleated Erythrocytes from Maternal Blood by Use of Short Tandem Repeat Sequences

Background: The purpose of this study was to determine whether aneuploid fetal nucleated erythrocytes (NRBCs) could be detected in maternal blood through the use of fluorescent PCR amplification with polymorphic short tandem repeat (STR) markers as an alternative or complementary method to analysis by fluorescent in situ hybridization (FISH).

Methods: Peripheral blood samples were obtained from women who had just undergone termination of pregnancy because of fetal trisomy 21 (three cases, 47,XY,+21; four cases, 47,XX,+21). Candidate fetal cells were isolated by flow-sorting by antibodies to the γ chain of fetal hemoglobin and Hoechst 33342. FISH analysis was performed by the use of chromosome-specific probes for X, Y, and 21. Fetal NRBCs, as defined by the presence of γ staining, characteristic morphology, and three chromosome 21 signals, along with maternal leukocytes, defined as γ negative and two chromosome 21 signals, were micromanipulated separately and subjected to fluorescent PCR amplification of chromosome 21 STR markers (D21S11, D21S1411, and/or D21S1412).

Results: In five of seven cases analyzed, fetal NRBCs were aneuploid, as determined by the presence of triallelic or diallelic peaks of chromosome 21 sequences when compared with sequences from the maternal leukocytes.

Conclusions: Fluorescent PCR amplification of STRs can detect fetal aneuploidy and may be useful in the setting of poor hybridization efficiency with FISH analysis. These results suggest that combined fetal aneuploidy and single-gene diagnoses by the use of DNA microarrays may be feasible in the near future.

Fetomaternal cellular and plasma DNA trafficking: the Yin and the Yang

In human pregnancy, multiple lines of evidence have indicated that there is trafficking of nucleated cells and cell-free DNA between the mother and fetus. Diagnostically, fetal cells in maternal blood and fetal DNA in maternal plasma offer a noninvasive source of fetal material for prenatal diagnosis. Through the developments of methods for fetal cell isolation and fetal DNA detection, many fetal genetic characteristics and chromosomal abnormalities have been detected from maternal blood. Large-scale clinical trials have been initiated that will facilitate the eventual application of these technologies. The presence of large quantities of cell-free fetal DNA in maternal plasma challenges the conventional belief that the fetal and maternal circulations are separate entities. In addition, the recent demonstration of the persistence of fetal cells following delivery also opens up a new field of investigation and raises new physiologic and pathogenic implications. Like the Yin and Yang in Chinese mythology, we believe that fetal cells and fetal DNA transfer are closely related and should be studied and applied in a synergistic manner.

Quantification of all fetal nucleated cells in maternal blood between the 18th and 22nd weeks of pregnancy using molecular cytogenetic techniques

Different types of nucleated fetal cells (trophoblasts, erythroblasts, lymphocytes, and granulocytes) have been recovered in maternal peripheral blood. In spite of many attempts to estimate the number of fetal cells in maternal circulation, there is still much controversy concerning this aspect. The numbers obtained vary widely, ranging from 1 nucleated cell per 104 to 1 per 109 nucleated maternal cells. The purpose of our project was to determine the absolute number of all different types of male fetal nucleated cells per unit volume of peripheral maternal blood. Peripheral blood samples were obtained from 12 normal pregnant women known to carry a male fetus between 18 and 22 weeks of pregnancy. Three milliliters (3 ml) of maternal blood has been processed without any enrichment procedures. Fluorescence in situ hybridization (FISH) and primed in situ labeling (PRINS) were performed, and fetal XY cells were identified (among maternal XX cells) and scored by fluorescent microscopy screening. The total number of male fetal nucleated cells per milliliter of maternal blood was consistent in each woman studied and varied from 2 to 6 cells per milliliter within the group of normal pregnancies. The number of fetal cells in maternal blood, at a given period, is reproducible and can therefore be assessed by cytogenetic methods. This confirms the possibility of developing a non-invasive prenatal diagnosis test for aneuploidies. Furthermore, we demonstrate that it is possible to repeatedly identify an extremely small number of fetal cells among millions of maternal cells.

Isolation of fetal cells from the maternal circulation: prospects for the non-invasive prenatal diagnosis

The research into non-invasive and invasive prenatal diagnostic techniques developed almost in parallel. On the one hand the need was arising to ensure the birth of normal progeny in all cases, while on the other, it was not possible to eliminate the abortion risks connected with the invasiveness of amniocentesis (risk of abortion 1/200), chorion villi sampling, (risk of abortion 2%) and funicolocentesis (risk of abortion 3-4%). One of the first researchers in the non-invasive field was Adinolfi who published the earliest data in 1974 on the possibility of detecting three types of fetal cells in the maternal circulation using flow cytometry. Adinolfi suggested the possibility of using fetal cells present in the maternal circulation for prenatal diagnosis of chromosome or biochemical anomalies. Our review takes into consideration the latest methodological and technical progress in relation to the study of fetal cells in maternal circulation, without considering cells present in the endocervical canal where from the 8th week of pregnancy it is only possible to obtain trophoblast cells. This technique has since been abandoned due to the scarcity of cellular material available, the greater risk of contamination by cells of maternal origin, and also because the recovery of the cells is unpredictable, despite their potential use for the early non-invasive diagnosis of sex. The following issues are addressed in this review: the characterization of the fetal cell types present in the maternal circulation, the methods of their separation and enrichment, and the methods of genetic diagnostics applied.