Genotipificación del gen RHD en ADN fetal libre en plasma de embarazadas RhD negativo / Genotyping of the RHD gene in free fetal DNA in plasma of RhD negative pregnant women

Objetivo: Determinar el grupo RhD fetal a través del estudio del gen RHD en ADN fetal que se encuentra libre en plasma de embarazadas RhD negativo. Método: Se analizó la presencia de los genes RHD, SRY y BGLO en ADNfl obtenido de plasma de 51 embarazadas RhD negativo no sensibilizadas, utilizando una qPCR. Los resultados del estudio genético del gen RHD se compararon con el estudio del grupo sanguíneo RhD realizado por método serológico en muestras de sangre de cordón, y los resultados del estudio del gen SRY fueron cotejados con el sexo fetal determinado por ecografía. Se calcularon la sensibilidad, la especificidad, los valores predictivos y la capacidad discriminativa del método estandarizado. Resultados: El gen RHD estaba presente en el 72,5% de las muestras y el gen SRY en el 55,5%, coincidiendo en un 100% con los resultados del grupo RhD detectado en sangre de cordón y con el sexo fetal confirmado por ecografía, respectivamente. Conclusiones: Fue posible deducir el grupo sanguíneo RhD del feto mediante el estudio del ADN fetal que se encuentra libre en el plasma de embarazadas con un método molecular no invasivo desarrollado y validado para este fin. Este test no invasivo puede ser utilizado para tomar la decisión de administrar inmunoglobulina anti-D solo a embarazadas RhD negativo que portan un feto RhD positivo.

Objective: To determine the fetal RhD group through the study of the RHD gene in fetal DNA found free in plasma of RhD negative pregnant women. Method: The presence of the RHD, SRY and BGLO genes in fetal DNA obtained from plasma of 51 non-sensitized RhD negative pregnant women was analyzed using qPCR. The results of the genetic study of the RHD gene were compared with the RhD blood group study performed by serological method in cord blood samples, and the results of the SRY gene study were compared with the fetal sex determined by ultrasound. Sensitivity, specificity, predictive values and discriminative capacity of the standardized method were calculated. Results: The RHD gene was present in 72.5% of the samples and the SRY gene in 55.5%, coinciding 100% with the results of the RhD group detected in cord blood, and with the fetal sex confirmed by ultrasound, respectively. Conclusions: It was possible to deduce the RhD blood group of the fetus through the study of fetal DNA found free in the plasma of pregnant women with a non-invasive molecular method developed and validated for this purpose. This non-invasive test can be used to make the decision to administer anti-D immunoglobulin only to RhD-negative pregnant women carrying an RhD-positive fetus.

Development of plasma quality control material for non-invasive prenatal detection of fetal aneuploidy / 中华检验医学杂志

Objective:To develop a self-made plasma quality control material for non-invasive prenatal testing (NIPT) and evaluate its performance.Methods:139 NIPT-negative maternal plasmas stored in the genetic department of Shaoxing maternal and child health hospital from January 1, 2019 to June 30, 2021 were divided into male groups (19 cases) and female groups (120 cases) according to the neonatal gender. 9360 cases from September 2020 to September 2021 were enrolled as clinical validation cases.First step, 200 μl plasma from a 47 years-old non-pregnant healthy women was used as a matrix. Different amounts (0.1, 0.2, 0.5, 2.5, and 5 μl) of positive DNA from fetal chromosome aneuploidy (T21, T18, T13) detection kit were added. The appropriate volume of positive DNA was 0.5 μl according to the test results. Second step,Plasma in male and female group was treated as matrix. 0.5 μl positive DNA was added per 205 μl. Plasma matrix from female group showed good repeatability and the sensitivity was 100%.Third step, evaluate the self-made plasma quality control material, including storage stability, matrix uniformity and repeatability, and the effect of different batch numbers of positive DNA, by calculating Z score and the CV of fetal DNA concentration (FF).Results:Plasma matrix from female group showed good repeatability and the sensitivity was 100%, while the sensitivity of male group was only 84%. The CV of FF in female matrix was 3.9% in the repetitive experiments. After adding 0.5 μl positive DNA, the mean FF of self-made positive plasma quality control was 5.63%±0.42%, Z values>6, and the CV was 7% after storage of three months. Considering the concentration variation of positive DNA in different lots, 1 μl of positive DNA should be added when the FF of positive DNA is lower than 10%.Used in 9360 clinical cases from September 2020 to September 2021, all positive plasma quality control materials showed positive results, and the positive predictive value of trisomy 21 was 100%.Conclusions:The NIPT self-made positive plasma quality control material has been successfully developed in this study. The preliminary experimental results show that it has good repeatability and stability, which is suitable for clinical application.

Knowledge, attitude and practices of obstetricians and gynecologists on non- invasive prenatal testing with cell free fetal DNA in a private tertiary hospital / Philippine Journal of Obstetrics and Gynecology

@#There are a number of novel prenatal cytoogenetic analysis tests for obstetricians and gynecologists on detecting aneuploidies. In the recent years, screening of pregnant patients with non-invasive prenatal testing (NIPT) is one. As the spread of genomic medicine and preventive obstetrics continue, it is prudent for obstetricians and gynecologists to accept and optimize new screening modalities, whenever available. Chromosomal abnormalities are common. Worldwide, one out of 150 live births may involve chromosomal abnormalities. The American College of Obstetrics and Gynecologists (ACOG) and American College of Medical Genetics recommend invasive and non ? invasive prenatal testing (NIPT)3. The invasive testing, however, carries risk for procedure ? related miscarriage. 4This favors NIPT which avoids the risk. The current state of NIPT in the Philippines, is it was only in January 2018, were a NIPT workshop was conducted by the Society of Maternal Fetal Medicine.6 First, due to the minimal studies on personalized and precision medicine on prenatal testing, hence the strong move to conduct this study. In an extensive literature search review in Herdin, a local database and archives of Philippine Obstetrics and Gynecology, none specified researches on non ? invasive prenatal testing. Second, in our country alone, there is no provision for national prenatal tests. In our institution, it was already introduced but with no uptake yet. Because of this gap, scantiness and non - uptake on NIPT locally, hence the conduct of this study. The study aimed to investigate on the obstetricians and gynecologists (OB-GYNs) knowledge, attitude towards and practices (KAP) about NIPT. Majority of the OBGYNs were knowledgeable, had positive attitude and were practicing NIPT. Strikingly, a fourth of the respondents were not comfortable in explaining NIPT. The researcher recommends that there is a need to conduct this study on a larger scale cross - sectional survey and multiple studies due to the paucity of data.

Highly Sensitive and Specific Detection of SRY Gene for Non-invasive Prenatal Diagnosis / 分析化学

By detecting SRY gene of cell-free fetal DNA ( cffDNA) in maternal peripheral blood, the sex of fetuses was determined, the risks of sex-linked genetic disorders were assessed and the birth rate of sick fetuses was decreased. A method of real-time polymerase chain reaction ( PCR) coupled with invader assay was established to detect SRY gene. This method possessed the advantages such as high sensitivity, high specificity and non-contaminated with closed tube detection. Under the optimized reaction conditions such as 250 nmol/L detection probes, 7. 5 U FEN1 enzyme, 0. 5 U Taq polymerase and 67℃ of annealing temperature in pre-amplification, the simulated samples as low as 4% ( 4 copies/μL ) were detected and two clinical samples with the gestation age of 9 weeks and 10 weeks were successfully detected. The detection results showed that this method could be used to detect SRY gene of cffDNA in maternal peripheral blood, providing an effective technique for clinical non-invasive prenatal diagnosis based on SRY gene.

Highly Sensitive and Specific Detection of SRY Gene for Non-invasive Prenatal Diagnosis / 分析化学

By detecting SRY gene of cell-free fetal DNA ( cffDNA) in maternal peripheral blood, the sex of fetuses was determined, the risks of sex-linked genetic disorders were assessed and the birth rate of sick fetuses was decreased. A method of real-time polymerase chain reaction ( PCR) coupled with invader assay was established to detect SRY gene. This method possessed the advantages such as high sensitivity, high specificity and non-contaminated with closed tube detection. Under the optimized reaction conditions such as 250 nmol/L detection probes, 7. 5 U FEN1 enzyme, 0. 5 U Taq polymerase and 67℃ of annealing temperature in pre-amplification, the simulated samples as low as 4% ( 4 copies/μL ) were detected and two clinical samples with the gestation age of 9 weeks and 10 weeks were successfully detected. The detection results showed that this method could be used to detect SRY gene of cffDNA in maternal peripheral blood, providing an effective technique for clinical non-invasive prenatal diagnosis based on SRY gene.

Evaluation of preferences of women and healthcare professionals in Singapore for implementation of noninvasive prenatal testing for Down syndrome

<p><b>INTRODUCTION</b>Invasive prenatal diagnosis (IPD) has long been used to prenatally diagnose Down syndrome (DS), but it is associated with a small risk of miscarriage. Noninvasive prenatal testing (NIPT) is a highly sensitive screening test using cell-free DNA in maternal blood for detection of DS without the risk of miscarriage, but it confers a small risk of false-positive and false-negative results. The implementation of these procedures into clinical practice requires an understanding of stakeholder preferences.</p><p><b>METHODS</b>A total of 69 health professionals (HPs) and 301 women took part in a discrete choice experiment (DCE) in which preferences for four prenatal test attributes - accuracy, time of results, risk of miscarriage and amount of information provided - were assessed. Conditional logit regression was used to analyse the data. Data on demographics and ranked preferences for test attributes was collected, and a direct choice question regarding NIPT, IPD or neither test was posed to participants.</p><p><b>RESULTS</b>The women showed a preference for test safety, whereas HPs prioritised test accuracy above all other attributes. When offered a direct choice of NIPT, IPD or neither test, women aged 35 years and older, those with previous miscarriage or who knew a child with DS were more likely to choose NIPT. Chinese women preferred NIPT, whereas Indian women preferred IPD.</p><p><b>CONCLUSION</b>Our data highlights the need for patient-specific counselling, taking into account previous experiences and cultural factors. Since women and HPs prioritise different test attributes, it is essential that HPs recognise these differences in order to provide non-biased counselling.</p>

A study on the noninvasive prenatal diagnosis of fetal blood type by maternal blood / 预防医学

Objective ToexplorethevalueofprenataldiagnosisoffetalABObloodgroupsinthepreventionofABO-HDN,andtoprovideevidenceforpreventionofABO-HDN.Methods Atotalof3777sampleswerecollectedfromthe pregnant women whose ABO blood group is O,and we detected the ABO blood group by serological method to detect the titerofIgGanti-Aandanti-Binthematernalblood.Results Amongthe3777samplescollectedfromthepregnant women whose ABO blood group is O ,the titer of IgG anti-A to anti-B was 1 to1 024 in 27 samples(0.7%),1∶51 2 in 97 samples(2.6%),1∶256 in 1 63 samples(4.3%),1∶1 28 in 285 samples(7.5%)and 1:64 in 603 samples(1 6%). We followed the pregnancy and newborn outcome of 769 case whose antibody titer of 1∶64 or more ,and compared the fetal ABO blood group with results of the titer of IgG anti -A and/or anti -B.A total of 641 patients (83.3%) was corresponding resistance against A or B,and 1 28 patients (1 6.6%)was not corresponding resistance against A or B.The higher the antibody titer,the higher incidence of neonatal ABO hemolytic disease occurred.We extracted the fetal free DNA of peripheral blood plasma in 30 pregnant women, and the genotypes of fetal ABO blood group were detected by the polymerase chain reaction-sequence specific primer (PCR-SSP),and all the experiment presented success.Conclusion ThetiterofIgGanti-Atoanti-Bcouldbeusedtopreventtheoccurrenceofhemolyticdiseaseofnewborn. Considering the interference factors,the fetal free DNA in the maternal circulation could be used to prenatally detect fetal ABO blood groups.

Noninvasive prenatal test for fetal chromosomal aneuploidies by massively parallel sequencing of cell-free fetal DNA in maternal plasma: The first clinical experience in Korea

PURPOSE: Noninvasive prenatal test (NIPT) by massively parallel sequencing (MPS) of cell-free fetal DNA in maternal plasma marks a significant advancement in prenatal screening, minimizing the need for invasive testing of fetal chromosomal aneuploidies. Here, we report the initial clinical performance of NIPT in Korean pregnant women. MATERIALS AND METHODS: MPS-based NIPT was performed on 910 cases; 5 mL blood samples were collected and sequenced in the Shenzhen BGI Genomic Laboratory to identify aneuploidies. The risk of fetal aneuploidy was determined by L-score and t-score, and classified as high or low. The NIPT results were validated by karyotyping for the high-risk cases and neonatal follow-up for low-risk cases. RESULTS: NIPT was mainly requested for two clinical indications: abnormal biochemical serum-screening result (54.3%) and advanced maternal age (31.4%). Among 494 cases with abnormal biochemical serum-screening results, NIPT detected only 9 (1.8%) high-risk cases. Sixteen cases (1.8%) of 910 had a high risk for aneuploidy: 8 for trisomy 21, 2 for trisomy 18, 1 for trisomy 13, and 5 for sex chromosome abnormalities. Amniocentesis was performed for 7 of these cases (43.8%). In the karyotyping and neonatal data, no false positive or negative results were observed in our study. CONCLUSION: MPS-based NIPT detects fetal chromosomal aneuploidies with high accuracy. Introduction of NIPT as into clinical settings could prevent about 98% of unnecessary invasive diagnostic procedures.

Noninvasive fetal RHD genotyping using cell-free fetal DNA incorporating fetal RASSF1A marker in RhD-negative pregnant women in Korea

PURPOSE: Conventional methods for the prenatal detection of fetal RhD status involve invasive procedures such as fetal blood sampling and amniocentesis. The identification of cell-free fetal DNA (cffDNA) in maternal plasma creates the possibility of determining fetal RhD status by analyzing maternal plasma DNA. However, some technical problems still exist, especially the lack of a positive control marker for the presence of fetal DNA. Therefore, we assessed the feasibility and accuracy of fetal RHD genotyping incorporating the RASSF1A epigenetic fetal DNA marker from cffDNA in the maternal plasma of RhD-negative pregnant women in Korea. MATERIALS AND METHODS: We analyzed maternal plasma from 41 pregnant women identified as RhD-negative by serological testing. Multiplex real-time PCR was performed by amplifying RHD exons 5 and 7 and the SRY gene, with RASSF1A being used as a gender-independent fetal epigenetic marker. The results were compared with those obtained by postnatal serological analysis of cord blood and gender identification. RESULTS: Among the 41 fetuses, 37 were RhD-positive and 4 were RhD-negative according to the serological analysis of cord blood. There was 100% concordance between fetal RHD genotyping and serological cord blood results. Detection of the RASSF1A gene verified the presence of cffDNA, and the fetal SRY status was correctly detected in all 41 cases. CONCLUSION: Noninvasive fetal RHD genotyping with cffDNA incorporating RASSF1A is a feasible, reliable, and accurate method of determining fetal RhD status. It is an alternative to amniocentesis for the management of RhD-negative women and reduces the need for unnecessary RhIG prophylaxis.

Diagnóstico prenatal no invasivo basado en ADN libre fetal: actualización

El descubrimiento del ADN libre fetal circulando en sangre materna ha revolucionado la práctica de la Obstetricia y cambiado el paradigma del diagnóstico prenatal. En los últimos 5 años hemos avanzado del tamizaje de aneuplodías con muchos falsos positivos a uno mucho más efectivo y con cifras de falsos positivos muy bajas. Este es, sin duda, el mejor método de tamizaje actual que se tiene en Obstetricia.

The discovery of cell free fetal DNA (cff-DNA) in maternal circulation has profoundly changed the clinical practice of Obstetrics and knocked down an old paradigm in prenatal diagnosis. Over the past five years screening for chromosomal abnormalities has moved from one with a high false positive rate into another more effective and at lower false positive rate. Undoubtedly, this test is the best effective screening tool in Obstetrics.

Noninvasive prenatal diagnosis ofβ-thalassemia by enriching cell-free fetal DNA in materal plasma / 中国病理生理杂志

AIM:To establish a kind of simple and efficient method for cell-free fetal DNA ( cff-DNA) enrich-ment and to investigate its range of applications and the advantages and disadvantages.METHODS:(1) The single nucleo-tide polymorphisms( SNPs) , which linked to paternalβ-thalassemia mutations, were screened.We analyzed the contact be-tween the SNPs inβ-thalassemia gene ( HBB gene) and haploid type by the Haploview software, and then selected these close SNPs which have higher heterozygosity with the HBB gene.(2) We selected 4 cases of different β-thalassemia muta-tions with their husband, and then we used TT-FAST-COLD-PCR to enrich the IVS-II-654 mutations in maternal plasma.If the IVS-II-654 mutation was not detected, we detected the SNP which linked to the IVS-II-654 mutation.Similarly, we used TT-FULL-COLD-PCR to enrich the CD41-42 mutations in the maternal plasma.At the same time, we used the conventional PCR to enrich CD41-42 mutation and IVS-II-654 mutation in the maternal plasma.RESULTS:(1) Nine cases of the SNP ( rs7480526) linked to the mutation at IVS-II-654 in HBB gene, and 11 cases of the SNP ( rs10768683) linked to the muta-tion at CD41-42 in HBB gene were detected.( 2 ) We detected 1 case who inherited the paternal β-thalassemia mutation (IVS-II-654).We did not directly detect patermal IVS-II-654 mutation in maternal plasma, but detected the SNP linked to the IVS-II-654 mutation in the other case and had 100%detection, and 2 cases inherited the paternal β-thalassemia muta-tions (CD41-42) in the maternal plasma by TT-FULL-COLD-PCR and had 100%detection.However, we detected nothing by conventional PCR.CONCLUSION:TT-COLD-PCR is applicable to enrich cell-free fetal DNA in maternal plasma and is a method in the field of noninvasive prenatal diagnosis.

Clinical application of non-invasive prenatal testing using cell free fetal DNA

Non-invasive prenatal testing using next generation sequencing technology with cell free fetal DNA from the blood of pregnant women has been rapidly adopted as a screening test for the detection of disorders involving chromosomal aneuploidy, especially Down syndrome. However as part of a prenatal recommendation in high-risk group, this laboratory assessment should be accompanied by informed counseling at both pre-test and post-test stages. In low-risk group and multifetal pregnancies, only conventional maternal serum screening tests in the first trimester and/or second trimester in addition to measurement of nuchal translucency should be recommended, until this potential tool has been incorporated into current screening strategic modalities on the basis ofsufficient published data.

Non-invasive prenatal diagnosis of fetal trisomy 21 using cell-free fetal DNA in maternal blood

Since the existence of cell-free fetal DNA (cff-DNA) in maternal circulation was discovered, it has been identified as a promising source of fetal genetic material in the development of reliable methods for non-invasive prenatal diagnosis (NIPD) of fetal trisomy 21 (T21). Currently, a prenatal diagnosis of fetal T21 is achieved through invasive techniques, such as chorionic villus sampling or amniocentesis. However, such invasive diagnostic tests are expensive, require expert technicians, and have a miscarriage risk approximately 1%. Therefore, NIPD using cff-DNA in the detection of fetal T21 is significant in prenatal care. Recently, the application of new techniques using single-molecular counting methods and the development of fetal-specific epigenetic markers has opened up new possibilities in the NIPD of fetal T21 using cff-DNA. These new technologies will facilitate safer, more sensitive and accurate prenatal tests in the near future. In this review, we investigate the recent methods for the NIPD of fetal T21 and discuss their implications in future clinical practice.

Noninvasive Prenatal Diagnosis using Cell-Free Fetal DNA in Maternal Plasma: Clinical Applications

Owing to the risk of fetal loss associated with prenatal diagnostic procedures (amniocentesis, chorionic villus sampling), noninvasive prenatal diagnosis (NIPD) is ultimate goal of prenatal diagnosis. The discovery of circulating cell-free fetal DNA (cffDNA) in maternal plasma in 1997 has opened up new probabilities for NIPD by Dr. Lo et al. The last decade has seen great development in NIPD. Fetal sex and fetal RhD status determination by cffDNA analysis is already in clinical use in certain countries. For routine use, this test is limited by the amount of cell-free maternal DNA in blood sample, the lack of universal fetal markers, and appropriate reference materials. To improve the accuracy of detection of fetal specific sequences in maternal plasma, internal positive controls to confirm to presence of fetal DNA should be analyzed. We have developed strategies for noninvasive determination of fetal gender, and fetal RhD genotyping using cffDNA in maternal plasma, using real-time quantitative polymerase chain reaction (RT-PCR) including RASSF1A epigenetic fetal DNA marker (gender-independent) as internal positive controls, which is to be first successful study of this kind in Korea. In our study, accurate detection of fetal gender through gestational age, and fetal RhD genotyping in RhD-negative pregnant women was achieved. In this assay, we show that the assay is sensitive, easy, fast, and reliable. These developments improve the reliability of the applications of circulating fetal DNA when used in clinical practice to manage sex-linked disorders (e.g., hemophilia, Duchenne muscular dystrophy), congenital adrenal hyperplasia (CAH), RhD incompatibility, and the other noninvasive pregnant diagnostic tests on the coming soon. The study was the first successful case in Korea using cffDNA in maternal plasma, which has created a new avenue for clinical applications of NIPD.

Diagnóstico prenatal no invasivo: Ácidos nucleicos de origen fetal en sangre materna / Non invasive prenatal diagnosis: Fetal nucleic acid analysis in maternal blood

Las técnicas actuales de diagnóstico prenatal de enfermedades génicas y cromosómicas incluyen procedimientos invasivos que conllevan un pequeño, pero significativo, riesgo. Por muchos años se ha estudiado la posibilidad de utilizar células fetales en circulación materna; sin embargo, ha fracasado su implementación clínica debido a su escasez y persistencia luego del parto. Desde hace más de una década se detectó ADN fetal libre en sangre de embarazadas. Este sería de origen placentario e indetectable después del parto, y fuente de material fetal para el desarrollo de técnicas diagnósticas utilizando sangre materna. No obstante, la mayoría del ADN libre en circulación materna es de origen materno con una contribución fetal del 3% al 6% aumentando a lo largo de la gestación. Dado que los métodos actuales no permiten separar el ADN libre fetal del materno, las aplicaciones se focalizan en el análisis de genes no presentes en la madre, tales como secuencias del cromosoma Y, o gen RHD en madres Rh negativas, o mutaciones paternas o de novo. Asimismo, la detección de ARN fetal libre en sangre de embarazadas abrió la posibilidad de obtener información acerca de patrones de expresión génica de tejidos embrionarios y, utilizando genes que se expresan sólo en la unidad feto-placentaria, se podría establecer un control de presencia de material fetal, independiente del material genético de la madre. El presente trabajo describe las evidencias acerca del pasaje de ácidos nucleicos fetales a circulación materna, su aplicación actual en el diagnóstico prenatal y posibles usos futuros.

Current prenatal diagnosis of monogeneic and chromosomal diseases, includes invasive procedures which carry a small but significant risk. For many years, analysis of fetal cells in maternal circulation has been studied, however it has failed its clinical use due to the scarcity of these cells and their persistance after delivery. For more than a decade, the presence of cell-free fetal DNA in maternal blood has been identified. These fetal DNA fragments would derive from the placenta and are not detected after delivery, making them a source of fetal material for carrying out diagnosis techniques using maternal blood. However, the vast majority of cell free DNA in maternal circulation is of maternal origin, with the fetal component contributing from 3% to 6% and rising towards term. Available methodologies do not allow separation of fetal from maternal cell free DNA, so current applications have been focused on the analysis of genes not present in the mother, such as Y chromosome sequences, or RHD gene in RhD-negative women, or paternal or de novo mutations. Also, the detection of cell-free fetal RNA in maternal blood offers the possibility of obtaining information regarding genetic expression profiles of embrionic tissues, and using genes expressed only at the feto-placental unit, controls for the presence of fetal material could be established, regardless of maternal genetic tissue. The present article describes the evidences regarding the passage of fetal nucleic acids to maternal circulation, its current prenatal diagnosis application and possible future perspectives.

Influence of delay in blood-processing on the level of cell-free fetal DNA in maternal plasma sample / 第二军医大学学报

Objective: To investigate the influencing factors of cell-free fetal DNA level in the maternal plasma during blood-processing. Methods: Aliquots of blood samples from pregnant women with male fetus were processed at 6 h and 36 h after sampling. The SRY and β-globin genes and the total DNA level were quantified by real-time quantitative PCR. Death of white blood cells was assayed by flow cytometry after stained with Annexin V/PI. The plasma DNase activity was assayed by radial enzyme-diffusion method and plasma lactate dehydrogenases (LDH) by rate method. Results: A 36 hour delay in blood-processing led to a significant increase in the total DNA and decrease in the fetal DNA (SRY gene) in the maternal plasma. The ratio of fetal DNA decreased from (10.3±5.6) % at 6 h after sampling to (3.0±2.1) % at 36 h after sampling under 4°C (P< 0.05). No dead cells were identified in the blood sample 6 h after sampling; however, apoptosis and necrosis of white blood cells were identified 36 h after sampling. The activity of LDH at 36 h was significantly higher than that at 6 h (P<0.05). Radial enzyme-diffusion result showed that, though greatly decreased at 4°C, the DNase was still able to degrade DNA. Conclusion: Delay in blood-processing can lead to increase of the total free DNA in maternal plasma but decrease of fetal DNA, which might be related to the death of white blood cells and degradation of fetal DNA by plasma DNase, so the extraction of fetal DNA should be done as early as possible after sampling (within 6 h).

Prenatal diagnosis value of free fetal DNA in maternal blood / 第二军医大学学报

The discovery of circulating fetal DNA paves a new way for non-invasive prenatal diagnosis. Examining the specific fetal DNA sequence of the circulating fetal DNA has been used for prenatal diagnosis of sex-linked disorders, fetal rhesus D blood typing and single gene inheritance disease. The variation of the circulating DNA levels can also be used for diagnosis of preeclampsia, premature delivery, and fetal chromosome disorders. This paper aims to review the biochemistry characters and clinical application of the circulating fetal DNA in maternal peripheral plasma.

Diagnóstico pré-natal utilizando sangue materno / Prenatal diagnosis using maternal blood

As técnicas de diagnóstico pré-natal têm evoluído de forma acelerada, em especial aquelas que implicam menor invasão fetal. Nesse cenário, grande importância tem sido dispensada às técnicas de detecção de DNA fetal livre (DNA-fl) no sangue materno, as quais apresentam melhor relação custo-benefício quando comparadas às técnicas de enriquecimento e isolamento de células fetais. O DNA-fl pode ser avaliado de forma qualitativa ou quantitativa. Na primeira forma, detectam-se seqüências gênicas fetais de herança exclusivamente paterna com o intuito de selecionar fetos portadores de determinada doença, como a mutação para a fibrose cística ou a identificação de características fetais diferentes das maternas, como a incompatibilidade sanguínea RhD. Assim, os recursos propedêuticos invasivos ficariam reservados apenas para uma pequena parcela dessa população. Na segunda forma, quantifica-se a concentração de DNA-fl para se definir gestantes sob risco para eventos desfavoráveis relacionados a alterações da interface materno-fetal, como abortamento, trabalho de parto pré-termo e pré-eclâmpsia. Cabe às instituições de atenção pré-natal terciária a pesquisa e a aplicação desses recursos, objetivando a redução dos custos e sua maior disponibilização para a sociedade, conseqüentemente oferecendo diagnósticos mais precoces e menores taxas de morbimortalidade materna e fetal.

Prenatal diagnostic techniques are evolving greatly, especially noninvasive procedures. Great importance have been given to the free fetal DNA (ff-DNA) detection in maternal blood presents better cost/benefits relation when compared to enrichment and isolation of fetal cells. The ff-DNA can be analyzed qualitatively or quantitatively forms. In the first form, the fetal paternally derived genetic sequences are detected in order to select which fetuses are affected by determined disease, as the mutation for cystic fibrosis, of to identify fetal characterístics different from his mother's, as in RHD incompatibility. Then, invasive procedures could only be used in part of this population aiming more therapeutics aspects than diagnosis. In the second form, the ff-DNA quantilication can define pregnancies under risk for undesirable outcomes related to anomalies in the maternal-fetal interface, such as abortion, preterm labor and pre-eclampsia. It's expected that tertiary prenatal care centers research can work with those procedures in order to offer early diagnosis and lowest rates of fetomaternal morbimortality.

Quantitative analysis of cell-free fetal DNA levels in maternal plasma with DOWN syndrome and normal pregnancies / 中国综合临床

Objective To investigate the application of real-time quantitative PCR in quantification of cell-free fetal DNA maternal plasma in patients bearing fetuses affected with DOWN syndrome. Methods Cell-free fetal DNA in maternal serum was isolated from 30 samples(7 male DOWN syndrome fetal ,3 female DOWN syndrome fe-tal,14 male euploid fetal,6 female euploid fetal). Cell-free fetal DNA levels in maternal serum were measured using real-time quantitative PCR using SRY as marker. Results The median cell-free fetal DNA levels in pregnant carry-ing male fetuses(n=7) and the controls (pregnant carrying male euploid fetuses,n=14)were 318.03±96.74 ge-nome-equivalents/ml and 154.40±39.43 genome-equivalents/ml of maternal serum,respectively (t=3.33,P=0.004 ),which was o in women with female fetuses. Conclusion The cell-free fetal DNA levels in pregnant women with DOWN syndrome fetuses are higher than that in pregnant women with normal fetuses.

Application of MiniSTR in the detection of fetal DNA in maternal plasma / 中国输血杂志

Objective To develop an efficient method for detecting the short tandem repeat(STR) of fetal DNA in maternal plasma by miniSTR technique.Methods A total of 9 blood samples form pregnant women from 11 to 27 weeks of gestation were collected.Each isolated total plasma DNA was amplified in single multiplex using the ABI MiniFilerTM kit,which could simultaneously genotype the 9 miniSTR loci,including D13S317,D7S820,D2S1338,D21S11,D16S539,D18S51,CSFIPO,FGA and Amelogenin,and the PCR products were detected by using ABI PrismTM 3100 DNA Sequencer.The allelic designation of each STR locus was accomplished using the GeneMapper ID 3.2 software.Results Father-origin fetal STR allele was detected in all the 9 plasma DNA samples.An average of 3.1 fetal STR alleles of the 8 autosomal STR loci was observed in each of the 9 plasma DNA samples.As for the Amelogenin locus,Amelogenin Y allele was detected in 5 plasma DNA samples from pregnancies with male fetus,and allelic peak height values were all over 50 RFU,according to ABI Mini FilerTM PCR conditions,and the ratio of Amelogenin Y allele peak height value to Amelogenin X allele peak height value was 8.45%.However,no Amelogenin Y allele was detected in other 4 plasma DNA samples from pregnant women with female fetus.Conclusion The miniSTR technique is suitable for STR genotyping using fetal DNA in maternal plasma,and it suggests a broad application in noninvasive molecular prenatal diagnosis.