Non-invasive prenatal rhesus D genotyping using cell-free foetal DNA

Background & objectives: Non-invasive prenatal diagnosis (NIPD) of rhesus D (RHD) genotype using cell-free foetal DNA is extensively used in many developed countries. Studies on NIPD from India are scarce. The aim of the present study was to evaluate the performance of non-invasive foetal RHD genotyping by targeting exon 10 of the RHD gene using cell-free DNA. Methods: DNA was extracted from the maternal plasma of alloimmunized and non-alloimmunized women between 7 and 34 wk of gestation. RHD sequence was determined by quantitative real time polymerase chain reaction (PCR). Results were compared with RhD phenotype obtained from cord blood samples of neonates. Results: A total of 135 samples from RhD-negative pregnant women were collected. The foetal RHD status was conclusive in all 135 (100%) cases. The highest number of cases reported for RHD genotyping were from Punjab (38.5%) followed by Haryana (24.4%), Himachal Pradesh (17.0%) and Chandigarh Union Territory (13.3%). The non-invasive test correctly predicted the foetal RhD phenotype in 133 of 135 cases, making the accuracy of the test as 98.51 per cent [95% confidence interval (CI): 97.90-99.50%]. The overall sensitivity and specificity of the test were 99.18 per cent (95% CI: 95.52-99.98%) and 92.31 per cent (95% CI: 63.97-99.81%), respectively, with negative and positive predictive values of 99.80 per cent (95% CI: 94.85-99.87%) and 96.31 per cent (95% CI: 62.87-98.84%), respectively. Interpretation & conclusions: Non-invasive foetal RHD determination by single-exon quantitative PCR exhibited high accuracy and could be used in routine clinical practice after confirmatory studies are done.

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.

Incorporación del estudio de ADN fetal en sangre materna al cribado de cromosomopatías / Incorporation of the study of fetal DNA in maternal blood to the screening of chromosomal diseases

OBJETIVO: Evaluar la efectividad del cribado combinado de primer trimestre para la detección prenatal de aneuploidías tras 6 años de implantación en nuestro servicio y su repercusión en la disminución de pruebas diagnósticas invasivas. Se propone establecer un protocolo para incorporar el estudio de ADN fetal en sangre materna a partir de las revisiones bibliográficas publicadas. MÉTODO: Se evaluó el riesgo de anomalía cromosómica fetal en 3177 gestaciones mediante cribado combinado de primer trimestre entre enero de 2011 y diciembre de 2014. Se revisaron las amniocentesis realizadas desde que se instauró el cribado combinado en 2008 comparándolas con las de los 5 años anteriores. RESULTADOS: La tasa de detección del cribado para trisomía 21 fue del 94,4% y la tasa de falsos positivos de 6,4%. En el año 2005 estábamos realizando 194 amniocentesis, tras 6 años de implantación del cribado, en el año 2013 se realizaron 35 amniocentesis lo que implica una disminución del 70%. CONCLUSIONES: El cribado combinado de primer trimestre ha demostrado una mayor tasa de detección para trisomía 21 que el cribado de segundo trimestre y/o la edad materna, además de que ha llevado a una importante reducción en el número de pruebas invasivas. En los próximos años la incorporación del estudio de ADN fetal mejorará la detección de aneuploidías, con una drástica disminución de las pruebas invasivas por lo que se hace necesario la implantación de nuevos protocolos.

AIMS: To evaluate the effectiveness of first trimester combined screening in the prenatal detection of aneuploidy after 6 years of implantation in our service and its impact in reducing invasive diagnostic tests. It is proposed to establish a protocol to incorporate the study of fetal DNA in maternal blood from published literature reviews. METHODS: The risk of fetal chromosomal anomalies was assessed in 3177 pregnancies with first trimester combined screening between January 2009 and December 2014. The amniocenteses performed were checked against those of the previous 5 years. RESULTS: The detection rate of screening for trisomy 21 was 94.4% and the false-positive rate was 6.4%. In 2005 there were 194 amniocenteses. In 2013, 5 years after the introduction of screening, 68 amniocenteses were performed, representing a 70% reduction in invasive procedures. CONCLUSIONS: First trimester combined screening has shown a higher detection rate for trisomy 21 that the second trimester screening and/or maternal age, and has substantially reduced the use of invasive prenatal diagnostics procedures. In the coming years, the incorporation of the study of fetal DNA improve the detection of aneuploidys with a drastic reduction of invasive tests so that, the implementation of new protocols is necessary.

SRY sequence in maternal plasma: Implications for non-invasive prenatal diagnosis: First report from India.

AIM: The presence of circulatory cell-free fetal DNA in maternal plasma has found new applications in non-invasive risk-free prenatal diagnosis. MATERIALS AND METHODS: We made use of a size separation approach along with real time polymerase chain reaction (PCR) to evaluate the use of fetal DNA in the detection of the sex of the fetus. Cell-free fetal DNA was isolated from the plasma of 30 women (10–20 weeks gestation) using a size separation approach. We made use of Taq Man Chemistry and real time PCR using primers and probes for GAPDH and SRY. RESULTS: Only 24 cases could be studied as there was no amplification in six cases. Fetal sex was accurately determined in all of the 24 cases wherein 19 women were carrying male fetuses and five women were carrying female fetuses. An increase in the amount of fetal DNA was observed with an increase in the gestational age. CONCLUSIONS: Real time PCR analysis is a highly sensitive and accurate tool for non-invasive prenatal diagnosis, allowing detection of the sex of the fetus as early as 10 weeks of gestation. Non-invasive prenatal diagnosis eliminates the risk of fetal loss associated with the invasive procedure.

Non-invasive Prenatal Diagnosis of Trisomy 21 by Dosage Ratio of Fetal Chromosome-specific Epigenetic Markers in Maternal Plasma / 华中科技大学学报（医学）（英德文版）

This study examined the methylation difference in AIRE and RASSF1A between maternal and placental DNA,and the implication of this difference in the identification of free fetal DNA in maternal plasma and in prenatal diagnosis of trisomy 21.Matemal plasma samples were collected from 388 singleton pregnancies,and placental or chorionic villus tissues from 112 of them.Methylation-specific PCR (MSP) and methylation-sensitive restriction enzyme digestion followed by fluorescent quantitative PCR (MSRE + PCR) were employed to detect the maternal-fetal methylation difference in AIRE and RASSF1A.Diagnosis of trisomy 21 was established according to the ratio of fetal-specific AIRE to RASSF1A in matemal plasma.Both methods confirmed that AIRE and RASSF1A were hypomethylated in maternal blood cells but hypermethylated in placental or chorionic villus tissues.Moreover,the differential methylation for each locus could be seen during the whole pregnant period.The positive rates of fetal AIRE and RASSF1A in maternal plasma were found to be 78.1％ and 82.1％ by MSP and 94.8％ and 96.9％ by MSRE + PCR.MSRE + PCR was superior to MSP in the identification of fetal-specific hypermethylated sequences (P＜0.05).Based on the data from 266 euploidy pregnancies,the 95％ reference interval of the fetal AIRE/RASSF1A ratio in maternal plasma was 0.33-1.77,which was taken as the reference value for determining the numbers of fetal chromosome 21 in 102 pregnancies.The accuracy rate in 98 euploidy pregnancies was 96.9％ (95/98).Three of the four trisomy 21 pregnancies were confirmed with this method.It was concluded that hypermethylated AIRE and,RASSF1A may serve as fetal-specific markers for the identification of fetal DNA in maternal plasma and may be used for noninvasive prenatal diagnosis of trisomy 21.

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.

Optimization of Conditions of Homologous Gene Quantitative Polymerase Chain Reaction / 中华医院感染学杂志

OBJECTIVE To evaluate the standard of non-invasive diagnosis of Down′s syndrome between the different PCR machines. METHODS Two kinds of PCR machines were used respectively to amplify the homologous genes-the human liver-like phosphofructokinase gene (PFKL) and the human muscle-like phosphofructokinase gene (PFKM). RESULTS The best annealing temperature of the two PCR machines were 64 ℃ and 60 ℃,and only in this reaction conditions PFKL′s and PFKM′s electrophoresis strips had the same optical density value. CONCLUSIONS This approach has proven that the conditions of amplified the PFKL and PFKM are different between the two kinds of PCR machines.