Foetal genetic diagnosis: development of techniques for early sampling of foetal cells

Recent trends in prenatal genetic screening and testing

Prenatal testing in recent years has been moving toward non-invasive methods to determine the fetal risk for genetic disorders without incurring the risk of miscarriage. Rapid progress of modern high-throughput molecular technologies along with the discovery of cell-free fetal DNA in maternal plasma led to novel screening methods for fetal chromosomal aneuploidies. Such tests are referred to as non-invasive prenatal tests (NIPTs), non-invasive prenatal screening, or prenatal cell-free DNA screening. Owing to many advantages, the adoption of NIPT in routine clinical practice was very rapid and global. As an example, NIPT has recently become a standard screening procedure for all pregnant women in the Netherlands. On the other hand, invasive sampling procedures remain important, especially for their diagnostic value in the confirmation of NIPT-positive findings and the detection of Mendelian disorders. In this review, we focus on current trends in the field of NIPT and discuss their benefits, drawbacks, and consequences in regard to routine diagnostics.

Traditional Prenatal Diagnosis: Past to Present

In the nearly 60 years since prenatal diagnosis for genetic disease was first offered, the field of prenatal diagnosis has progressed far past rudimentary uterine puncture to provide fetal material to assess gender and interpret risk. Concurrent with the improvements in invasive fetal sampling came technological advances in cytogenetics and molecular biology that widened both the scope of genetic disorders that could be diagnosed and also the resolution at which the human genome could be interrogated. Nowadays, routine blood work available to all pregnant women can determine the risk for common chromosome abnormalities; chorionic villus sampling (CVS) and amniocentesis can be used to diagnose nearly all conditions with a known genetic cause; and the genome and/or exome of a fetus with multiple anomalies can be sequenced in an attempt to determine the underlying etiology. This chapter will discuss some of the major advances in prenatal sampling and prenatal diagnostic laboratory techniques that have occurred over the past six decades.

Noninvasive Prenatal Testing - When Is It Advantageous to Apply

Nowadays it is common sense in obstetrics that an increased risk for pregnancy loss due to invasive testing does not exist. Nonetheless, noninvasive prenatal testing (NIPT) is a hot topic, even though this approach does not provide a reduction of unintentionally induced abortions. NIPT has a number of shortcuts which are highlighted in this review, including: (1) in NIPT placental rather than fetal DNA is studied, (2) NIPT fails in 2–6% of cases, and (3) trisomy 21 accounts for only ∼50% of existing chromosomal aberrations. Thus, we agree with the literature that NIPT is a fascinating possibility to gain information on unborn life from minimal amounts of DNA. However, it remains a pure risk estimation test directed towards the detection of specific chromosomal abnormalities from peripheral blood of the pregnant woman. It is important to highlight that families buying this test, and getting a normal result, may be provided with a false sense of security. Thus, careful and comprehensive genetic counselling should be performed before the test is offered, and should include a clear explanation of the advantages and disadvantages, as well as limitations, compared to other methods.

The Japanese male: Female birth ratio rose in the 1966 Fire-Horse year due to female birth year misrepresentation

INTRODUCTION

The sex ratio at birth (usually denoted as M/T=male divided by total births) is influenced by cultural factors. The Chinese Zodiac holds that women born in the Fire Horse year (1966) would be unlucky. It has been shown that significantly less children were born in Japan in this year. This study was carried out in order to ascertain whether this year was also associated with any change in M/T.

METHODS

Annual male and female live births were obtained from a World Health Organization Mortality database for 1966±16years.

RESULTS

This study analysed a total of 58922297 births over the period 1950-82 (M/T 0.5146). The 1966 dip in total births was associated with a highly significant spike in M/T in the same year of 0.5184 (p<0.0001). 1965 and 1967 showed significant reductions from baseline M/T (p<0.0001). The periods immediately before and after 1965-67 showed higher baseline M/T (p≤0.008).

DISCUSSION

Sex blind strategies (contraception and abortion) have been shown to be responsible for the decline in total births. The increase in M/T in 1966 with a significant decline in M/T in 1965 and 1967 may be due to deliberate misattribution of birth year for female babies. M/T follows a U-shaped regression on cycle day of insemination. The higher M/T just before and after 1965-1967 may be due to higher coital rates in couples attempting to have a baby outside the Fire Horse year.

Implementation of high resolution whole genome array CGH in the prenatal clinical setting: advantages, challenges, and review of the literature

Array Comparative Genomic Hybridization analysis is replacing postnatal chromosomal analysis in cases of intellectual disabilities, and it has been postulated that it might also become the first-tier test in prenatal diagnosis. In this study, array CGH was applied in 64 prenatal samples with whole genome oligonucleotide arrays (BlueGnome, Ltd.) on DNA extracted from chorionic villi, amniotic fluid, foetal blood, and skin samples. Results were confirmed with Fluorescence In Situ Hybridization or Real-Time PCR. Fifty-three cases had normal karyotype and abnormal ultrasound findings, and seven samples had balanced rearrangements, five of which also had ultrasound findings. The value of array CGH in the characterization of previously known aberrations in five samples is also presented. Seventeen out of 64 samples carried copy number alterations giving a detection rate of 26.5%. Ten of these represent benign or variables of unknown significance, giving a diagnostic capacity of the method to be 10.9%. If karyotype is performed the additional diagnostic capacity of the method is 5.1% (3/59). This study indicates the ability of array CGH to identify chromosomal abnormalities which cannot be detected during routine prenatal cytogenetic analysis, therefore increasing the overall detection rate. In addition a thorough review of the literature is presented.

Preparation of chorionic villus samples for metaphase chromosome analysis and chromosomal microarray analysis

Chorionic villi are composed of an outer layer of trophoblastic cells and an inner mesenchymal cell core. They can be prepared for chromosome analysis using a culture method wherein villi are disaggregated by mechanical and enzymatic methods and the resulting cell suspension is used to establish primary cultures. Mesenchymal cells of the villus core are released by this procedure and the fibroblasts are actively proliferative in tissue culture. Cultures can be used for cytogenetic analysis after ∼1 week. Slides prepared by this technique can be stained using trypsin-Giemsa banding and analyzed for chromosomal abnormalities in fetal tissue. Chorionic villi may also be assessed by chromosomal microarray analysis (CMA). For this purpose, a method for extraction of high-quality DNA from CVS tissue is also described here.

Preparation of metaphase spreads from chorionic villus samples

Chorionic villi are composed of an outer layer of trophoblastic cells and an inner mesenchymal cell core, both of fetal origin. Cytogenetic analysis of chorionic villi can be accomplished using material prepared in either of two ways. In the culture method described in this unit, villi are disaggregated by mechanical and enzymatic methods, and the resulting cell suspension is used to establish primary cultures. Mesenchymal cells of the villus core are released by this procedure and the fibroblasts are actively proliferative in tissue culture. Cultures can be used for cytogenetic analysis after 1 week. In the "direct" technique, presented here in an Alternate Protocol, Langhans cells of the cytotrophoblast, actively dividing cells in first-trimester villi, are synchronized and arrested in mitosis after a short incubation period, and metaphase spreads are prepared. Chorionic villi are composed of an outer layer of trophoblastic cells and an inner mesenchymal cell core, both of fetal origin.

Diagnóstico pré-natal

O presente artigo apresenta uma descrição de todos os métodos de diagnóstico pré-natal de anormalidades genéticas e cromossômicas, bem como dos relativos a doenças infecciosas na gravidez. O autor discute as diferenças entre eles, e as novas ferramentas da biologia molecular que são aplicadas nesses diagnósticos. Ao final é feita uma descrição da técnica de diagnóstico pré-implantação e de seu uso in vitro em laboratórios de fertilidade situados a mais de dois mil quilômetros um do outro.

Chorionic villus sampling by biopsy forceps. Results of 1580 procedures from a single centre

The results of a prospective series of 1580 chorionic villus sampling (CVS) procedures using biopsy forceps are presented. Most of the procedures (1442), including 11 sets of twins, were performed by the transcervical approach (TC-CVS), using a curved-shank thin forceps, and 138 by the transabdominal approach (TA-CVS), using a trocar-guided straight thin forceps. The mean gestational age for TC-CVS was 10.9 weeks, and in 233 cases (16 per cent) the procedure was carried out between the 12th and 14th weeks. The mean gestational age for TA-CVS was 16.7 weeks. The major indication for CVS was advanced maternal age (92.7 per cent in the TC and 91.8 per cent in the TA approach), and indications for abnormal ultrasound findings were more common in the TA approach (4.5 per cent) than in TC-CVS (0.07 per cent). Although sampling was apparently accomplished in all the procedures, in 3.1 per cent of the TC-CVS and 2.2 per cent of TA-CVS procedures, the samples were less than 1 mg after dissection. A cytogenic report was obtained in 96.1 per cent of the TC-CVS and 90.6 per cent of the TA-CVS. Maternal serum alpha-fetoprotein (MSAFP) was measured before and after TC-CVS and the post-CVS MSAFP was positively correlated with the sample weight. Second-trimester amniocentesis following CVS was required in 5.2 per cent (TC-CVS) and 6.5 per cent (TA-CVS), due to the failure to obtain a cytogenetic report or diagnostic confirmation. The follow-up to the 20th week was 100 per cent by ultrasound scan, and 88.6 per cent from the 21st week to 1 week after delivery. Fetal loss rates within 2 weeks of the procedure were 1.7 per cent (TC-CVS) and 0.8 per cent (TA-CVS) and total fetal loss accumulated to 1 week after delivery was 4.6 per cent (TC-CVS) and 5.9 per cent (TA-CVS). Factors found to increase significantly fetal loss in the TC-CVS series were maternal age and the collection of very small samples, but not the number of forceps insertions.

Chorionic villus sampling: quality control--a continuous improvement model

OBJECTIVE

Our purpose was to describe Vanderbilt University Medical Center's experience in establishing a chorionic villus sampling program and the importance of quality control along with a continuous improvement model on the first 1000 cases.

STUDY DESIGN

A continuous improvement model was established with emphasis on a multidisciplinary team approach and quality assurance process. A computerized data base was used for continuing analysis of complications and for allowing facile access to pertinent information.

RESULTS

A continuous improvement model allowed for an improved process and outcome for patients, personnel, and referring health care providers. Follow-up for initial symptoms after chorionic villus sampling was obtained on 98.5% of patients. Pregnancy follow-up, including birth data, was obtained on 93%.

CONCLUSION

A continuous improvement mode from the project's onset resulted in an improved process and outcome, information helpful for accessing spontaneous abortion rates and pregnancy outcomes (including the incidence of limb abnormalities and factors associated with abortions) and recommendations for training personnel.

Transabdominal chorionic villus sampling: analysis of 350 consecutive cases

We report a series of 350 patients submitted to transabdominal chorionic villus sampling (CVS). A technique using two ultrasound-guided needles and a suction pump was used. In most cases, the procedure was performed between 9 and 13 weeks. Twenty-one pregnancies were selectively terminated; nine spontaneous abortions followed the procedure and one fetal loss after 28 weeks was recorded; 153 pregnancies are in progress and 169 delivered fetuses are alive and well. Transabdominal biopsy is a feasible and effective technique for CVS.

Prenatal cytogenetic diagnosis after transabdominal chorionic villus sampling in the first trimester

First trimester prenatal cytogenetic diagnosis was attempted in 350 pregnancies after transabdominal chorionic villus sampling. The cytogenetic investigation was performed using both a short-term method (24 h incubation) and cell culture. Adequate samples were obtained in 99.1 per cent and in all these cases the fetal karyotype was established. A chromosome abnormality was found in 2.0 per cent of cases. A discrepancy between the karyotype obtained after 24 h incubation and the karyotype in cell culture was observed in 2.3 per cent. Maternal cell contamination in the cultures was confirmed in 13 of 181 cases where the 24 h incubation revealed a male karyotype. Studies of culture morphology showed that colonies of convoluted cells may serve as a marker for contamination with maternal cells in culture. For the present, we recommend using a short-term method as well as cell culture for cytogenetic investigation until the problems with karyotype discrepancy and maternal cell contamination have been further clarified.

Techniques of chorion villus sampling

Whilst randomized studies into the safety of chorionic villus sampling (CVS) are already under way the technique is now offered as an acceptable alternative to amniocentesis in many diagnostic centres. In counselling, the obstetrician can now quote a risk to the pregnancy of 2-4% which, even if the inevitable losses before 16 weeks are excluded, represents probably at least twice the risk of amniocentesis. The evolution of the obstetric procedures has meant that the transcervical approach to CVS has been the most popular to date but there is now increasing interest in transabdominal aspiration as it minimizes the possibility of infection. The two best known transcervical methods are aspiration with a plastic or metal cannula and biopsy with rigid forceps. The majority of aspirations have been performed using the Portex cannula technique. Using this, three centres (Milan, Chicago and Philadelphia) have had experience of over 5000 cases with a failure rate of less than 1% and a minimal fetal loss of 2.2%. However, the proportion of fetal losses may be between 4 and 7% by the time complete obstetric follow-up is available (Brambati et al, 1985). A similar technique has been used with a variety of cannulae. The experience of the first 1000 cases from San Francisco (Hogge et al, 1986) led them to conclude that CVS by this technique was acceptably safe but that continuing investigation was needed before CVS was offered routinely as an alternative to amniocentesis. The only other transcervical technique that is practical for routine use is biopsy with rigid forceps. The failure and fetal loss rates associated with this method are comparable to the aspiration technique. The pioneering work of Hahnemann and his colleague Smidt-Jensen has established transabdominal aspiration as a reliable alternative approach. Its main advantage should be to minimize the risk of infection which is inherent in all transcervical techniques. In addition, it does not need to be confined to 9-11 weeks gestation and thus offers couples the possibility of diagnosis between 12 and 14 weeks rather than waiting for amniocentesis at 16 weeks. The quality and quantity of the sample depends on the size of the needle used and the technique is said to have high patient acceptability. Nevertheless, fetal losses occur following the procedure (1.8-3.2%) and it may not always be successful (failure rate 1.9-4.2%).

Risks of chorion villus sampling

From the experience accumulated in less than 4 years of chorionic villus sampling activity, much has been learned about the advantages of prenatal diagnosis in the first trimester. The safety of the procedure during this developmental stage has been extremely good. The record in this centre with over 2700 cases sampled and over 2000 deliveries has demonstrated a fetal loss rate similar to that observed in amniocentesis studies. It appears that fetal loss that may be attributed to the procedure is not more than 1% and may be less. Some of that loss appears to be correlated with avoidable trauma to the chorionic membrane area. If this conclusion is valid, then avoidance of this pattern even in the occasional difficult case may further improve the already acceptable safety record of the procedure.

First trimester chorionic villi sampling and direct chromosome preparations

Chorionic villi sampling was performed on 52 patients prior to elective termination of their pregnancies. Villi were obtained in 42, and direct chromosome preparations were successful in 41 of them. The use of a mixture of 0.075 M potassium chloride and 1% sodium citrate in the ratio of 2:1 for hypotonic treatment and 40% acetic acid for cell dispersal yielded chromosomes with good morphology and G-bands.

Chorionic villus sampling

Chorionic villus sampling in the first trimester of pregnancy has the potential to become a major tool in the prenatal diagnosis and therapy of genetic disorders. Villus samples can be used for cytogenetic and biochemical studies as well as DNA analysis. However, little is known about the effects of chorionic villus sampling on a continuing pregnancy, or the long-term effects on the subsequently delivered infants. Despite these limitations, chorionic villus sampling appears to be a major breakthrough in prenatal diagnosis.

Prenatal diagnosis by chorionic villus sampling: lessons of the first 600 cases

Chorionic villus sampling (CVS) has emerged as a first trimester alternative to amniocentesis for the prenatal detection of genetic disorders. We report our experience in 600 consecutive CVS procedures to better delineate the safety, efficacy and reliability of this new method of prenatal diagnosis. Adequate samples were obtained at the initial visit in 97 per cent of the cases, and successful cultures were established in 98.7 per cent of these patients. Chromosome abnormalities were detected in 5.9 percent of those pregnancies tested because of advanced maternal age (greater than or equal to 35 years). A discrepancy between the villus karyotype and that of the fetus was found in 2.0 per cent of cases, and most commonly consisted of mosaicism in the villus sample for a chromosomal abnormality that was not found in fetal samples. The risk of spontaneous abortion following the procedure was 6.3 per cent. We conclude that chorionic villus sampling is an acceptably safe and reliable procedure, but further investigation is needed before it can become an established technique in prenatal diagnosis.

Prenatal diagnostic techniques. Chorionic villus sampling

Chorionic villus sampling (CVS) is a new prenatal diagnostic technique which is performed in the first trimester of pregnancy. Traditional methods of prenatal diagnosis, including amniocentesis and fetoscopy, must be performed in the midtrimester. In concert with the development of DNA methods of fetal cell analysis, first trimester fetal diagnosis utilizing CVS offers many advantages over traditional mid-trimester techniques. In addition, CVS may potentially allow therapeutic intervention to prevent or ameliorate some congenital defects.

Chorionic villi sampling: clinical experience, immediate complications, and patient attitudes

To develop chorionic villi sampling as a procedure for prenatal diagnosis, a pilot study was undertaken to perfect the obstetric and laboratory techniques, to evaluate our success with the procedure in continuing pregnancies, and to assess the attitudes of potential users of the procedure. Women about to have elective first-trimester abortions for nongenetic reasons were enrolled in the first phase of the study. Of the patients with a positive pregnancy test, 12.4% were found to have a nonviable pregnancy on ultrasound examination. Samples adequate for cytogenetic analysis were obtained in 130 of the 155 remaining cases, and the success rate was 93% in the 100 most recent cases. Direct cytogenetic analysis was undertaken in those cases successfully sampled, and karyotypes could be prepared in 97%. Immediate complications occurred in 5% of the pregnancies. Eight women at risk of bearing a child with a genetic defect had diagnostic chorionic villi sampling. Cytogenetic analysis was performed successfully on all of them. One had an induced abortion following the procedure because of the fetal diagnosis (a male with a 50% risk of Duchenne's muscular dystrophy). The other pregnancies are continuing uneventfully at 22 to 35 weeks' gestation. Finally, from preliminary analysis of our survey of potential users it appears that women 35 years old or over would prefer chorionic villi sampling to amniocentesis if the risks of the sampling were known to be low.

Chorion villi sampling (CVS) for prenatal diagnosis of genetic disorders: first results and future research

Chorion villi sampling (CVS) in the first trimester of pregnancy has become available recently as an alternative method to second trimester amniocentesis for prenatal diagnosis of genetic defects. Currently there are six different tissue sampling techniques being investigated in different centers around the world, but there are very few trials in ongoing pregnancies. From chorionic villi material cytogenetic and biochemical studies as well as DNA analyses can be performed. Different methods of chromosome analysis are being investigated at the University of California San Francisco and elsewhere to determine the most efficient and reliable techniques. Larger studies will be needed to establish the efficacy and the safety of the chorionic villi sampling procedure for the mother and the developing fetus. Although CVS is preferable to amniocentesis for psychological and medical reasons (earlier elective termination of a fetus with a genetic disorder), many questions remain to be answered in carefully controlled studies.

Antenatal diagnosis

The diagnosis of genetic disease in utero in early pregnancy is a new and exciting development with important applications in the management of families with a high risk of producing a child with an hereditary disorder. Techniques currently under investigation are briefly reviewed and include sex chromatin, cytogenetic and biochemical studies on amniotic fluid cells and the biochemical composition of amniotic fluid. The study of amniotic fluid and its contained cells would seem to offer a promising and important approach to the prevention of genetic disease.