Non-invasive prenatal diagnosis using fetal cells in maternal blood

Non invasive prenatal diagnosis of aneuploidy: next generation sequencing or fetal DNA enrichment?

Current invasive procedures [amniocentesis and chorionic villus sampling (CVS)] pose a risk to mother and fetus and such diagnostic procedures are available only to high risk pregnancies limiting aneuploidy detection rate. This review seeks to highlight the necessity of investing in non invasive prenatal diagnosis (NIPD) and how NIPD would improve patient safety and detection rate as well as allowing detection earlier in pregnancy. Non invasive prenatal diagnosis can take either a proteomics approach or nucleic acid-based approach; this review focuses on the latter. Since the discovery of cell free fetal DNA (cffDNA) and fetal RNA in maternal plasma, procedures have been developed for detection for monogenic traits and for some have become well established (e.g., RHD blood group status). However, NIPD of aneuploidies remains technically challenging. This review examines currently published literature evaluating techniques and approaches that have been suggested and developed for aneuploidy detection, highlighting their advantages and limitations and areas for further research.

Progress in heritable skin diseases: translational implications of mutation analysis and prospects of molecular therapies*

Epidermolysis bullosa, a group of blistering disorders, serves as the paradigm of the tremendous progress made in understanding the molecular genetics of heritable skin diseases. Mutations in 10 distinct genes have been disclosed in the classic forms of epidermolysis bullosa, and the level of expression of the mutated genes within the cutaneous basement membrane zone, the types and combinations of mutations and their consequences at the mRNA and protein levels, when placed in the context of the individual's genetic background and exposure to environmental trauma, all determine the subtype and the phenotypic severity in each case. The translational implications of mutation analysis include improved diagnosis and subclassification, refined genetic counseling of families at risk, and development of DNA-based pre natal and preimplantation genetic diagnosis. The prospects of molecular therapies for epidermolysis bullosa include further development of strategies for gene therapy, protein replacement therapy and cell-based therapies, including stem cell therapy and bone marrow transfer. Collectively, advances in the molecular genetics of heritable skin diseases clearly emphasize the value of basic research for improved diagnostics and patient care for genetic skin diseases.

A monoclonal antibody with potential for aiding non-invasive prenatal diagnosis: utility in screening of pregnant women at risk of preeclampsia

The development of a non-invasive method of prenatal diagnosis in maternal blood has been the goal of our investigations during the last years. We have developed several anti-CD71 monoclonal antibodies and optimized a protocol for the isolation of nucleated red blood cells (NRBC) from peripheral maternal blood. The enhanced traffic of fetal erythroblasts into the maternal circulation in preeclampsia has been investigated by several groups. In this study, we compared one of our antibodies, 2F6.3, with a commercial anti-CD71 antibody in blood samples from pregnant women suffering pregnancy-induced hypertension (PIH) and in a control group of pregnant women without clinical features suggestive of an increased risk of developing preeclampsia. The mAb 2F6.3, developed by our group, has succeeded in isolating a significantly higher number of erythroblasts with less maternal cell contamination than the commercial antibody in both women with PIH and in the control group (p<0.01; Wilcoxon Signed Ranks Test). Fluorescence in situ hybridization analysis also demonstrated that 2F6.3 is a better antibody for the isolation of fetal NRBC in maternal blood than the commercial anti-CD71 antibody.

Microchimerism and scleroderma: an update

Microchimerism has been defined by the presence of a low number of circulating cells transferred from one individual to another. This transfer takes place naturally during pregnancy, between mother and fetus, or between fetuses in multigestational pregnancies. Furthermore, the establishment of microchimerism can also occur during blood transfusion, as well as during bone marrow and solid-organ transplants. Recently, microchimeric cells have been implicated in the pathogenesis of autoimmune diseases, particularly systemic sclerosis. Studies have demonstrated an increased presence of microchimeric cells in peripheral blood and tissues from patients with systemic sclerosis, and, more recently, microchimeric cells were demonstrated to be specifically activated and capable of recognizing patient human leukocyte antigens.

[What's new in fetal medicine?]

One of the major progress in fetal medicine in recent years is the increased sensitivity of sonographic screening for foetal malformations, due to technical improvement but also to a better training of professionals. Screening for chromosomal abnormalities is no longer based on maternal age alone. Second trimester maternal serum screening (MSS) is increasingly used: thus in 1997, 376,798 MSS tests were performed in France, yielding to the prenatal diagnosis of 391 cases of Down's syndrome. First trimester sonographic nuchal translucency measurement (NTM) is an effective screening method when performed under stringent conditions. Quality control however, is more difficult to implement on a large scale for NTM than for MSS. Performing screening tests sequentially carries a danger of generating an unnecessarily high number of amniocentesis, which may be obviated by a rational calculation of an individual's risk to carry an aneuploid baby. First trimester MSS is expected to become standard practice in the next years, probably in combination with NTM. Cytogenetics underwent substantial innovations recently, due to the ever-increasing use of molecular cytogenetics. FISH techniques allow: 1) precise analysis of unexpected structural chromosomal abnormalities diagnosed by routine amniocentesis, 2) rapid screening of the most common aneuploidies by amniocentesis when a fetal structural anomaly is detected by 3rd trimester ultrasound, 3) diagnosis of micro-deletions suspected by fetal ultrasound or post-mortem. Prenatal diagnosis by maternal blood sampling and fetal cells or DNA analysis is now part of routine clinical practice in selected cases, such as fetal sexing in families affected by an X linked disease. Thus one can select those pregnancies eligible to invasive prenatal diagnosis. Pre implantation diagnosis, which has not been legal in France until 1999 is now increasingly used as an alternative to first trimester diagnosis. As for fetal therapy, a major recent breakthrough is the prenatal management of twin to twin transfusion syndrome by either amnioreduction or laser coagulation of inter-twin vascular shunts. In addition, new pathophysiologic concepts involving the renin angiotestin system could lead to further therapeutic innovations. A European randomised trial is now being completed to establish the respective indications of drainage and Laser. All this underscores that fetal medicine is no longer solely a succession of dramatic technical breakthroughs, but is entered an era of large-scale diffusion that requires evidence based evaluation.

Fetal DNA in maternal plasma

Recently, cell-free fetal DNA has been found in maternal plasma and serum. This discovery opens up a new field of investigation and provides an easily accessible source of fetal genetic material for prenatal diagnosis. Prenatal diagnostic applications of fetal DNA in maternal plasma include the investigation of sex-linked disorders and fetal rhesus D status determination. Cell-free fetal DNA has been found to be present in much higher fractional concentrations than fetal nucleated cells in maternal blood. The concentration of fetal DNA increases throughout pregnancy, with a sharp rise towards the end of gestation. Abnormally high levels of cell-free DNA have been found in pregnancies complicated by preeclampsia and preterm labor, an observation that has potential diagnostic and pathophysiologic implications. Much remains to be learned regarding the mechanisms of production and clearance of maternal plasma fetal DNA. It is hoped that the eagerly awaited answers to these and other questions may ultimately enhance our understanding of the fetomaternal relationship.

Influence of gestational age on fetal deoxyribonucleic acid retrieval in maternal peripheral blood

OBJECTIVE

We wanted to verify whether gestational age influences the retrieval of fetal deoxyribonucleic acid in maternal blood to identify the best period for maternal blood sampling for a future noninvasive prenatal diagnoses.

STUDY DESIGN

We amplified 81 deoxyribonucleic acid samples extracted from the peripheral blood of 27 pregnant women (18 bearing male fetuses and 9 bearing females) by nested polymerase chain reaction of the Y-specific sequence DYS14. We obtained three blood samples (one per gestational trimester) from each woman. Statistical evaluation was assessed by the McNemar test of symmetry.

RESULTS

Polymerase chain reaction results in male-bearing pregnancies differed significantly between the first and second trimesters and between the second and third trimesters (p < 0.025) in parallel with a decrease in sensitivity in the second trimester (67%) compared with the first (94%) and third trimesters (100%).

CONCLUSIONS

The drop in sensitivity from the first to the second trimester witnesses a variable concentration of fetal cells in maternal blood, with a negative balance in the second trimester. Therefore, to achieve an adequate polymerase chain reaction accuracy, the choice of gestational age is relevant and the first trimester seems to be more suitable than the second trimester.