Early fetal sex determination using a fluorescent DNA nanosensing platform capable of simultaneous detection of SRY and DYS14 sequences in cell-free fetal DNA

Early fetal sex determination is of crucial importance in the management of prenatal diagnosis of X-linked genetic abnormalities and congenital adrenal hyperplasia. The development of an efficient and simple method for high-sensitivity, affordable, and rapid screening of cell-free fetal DNA (cffDNA) is crucial for fetal sex determination in early pregnancy. In this study, single- and dual-fluorophore DNA biosensors based on multi-walled carbon nanotubes (MWCNT) were fabricated for the individual and simultaneous detection of the SRY gene and DYS14 marker in cffDNA obtained from maternal plasma samples. This nanosensing platform is based on the immobilization of single-stranded DNA (ssDNA) probes, labeled with ROX or FAM fluorophores, on MWCNT, resulting in the quenching of fluorescence emission in the absence of the targets. Upon the addition of the complementary target DNA (ctDNA) to the hybridization reaction, the fluorescence emission of fluorophore-labeled probes was significantly recovered to 79.5 % for ROX-labeled probes (i.e. SRY-specific probes), 81.5 % for FAM-labeled probes (i.e. DYS14-specific probes), and 65.9 % for dual-fluorophore biosensor compared to the quenching mode. The limit of detection (LOD) for ROX, and FAM was determined to be 4.5 nM, and 7.6 nM, respectively. For dual-color probes, LOD was found to be 5.4 (ROX) and 9.2 nM (FAM). Finally, the clinical applicability of the proposed method was confirmed through the detection of both biomarkers in maternal plasma samples, suggesting that the proposed nanosensing platform may be useful for the early detection of fetal sex using cffDNA.

Nanoparticle-Enhanced Surface Plasmon Resonance Imaging Enables the Ultrasensitive Detection of Non-Amplified Cell-Free Fetal DNA for Non-Invasive Prenatal Testing

Although many potential applications in early clinical diagnosis have been proposed, the use of a surface plasmon resonance imaging (SPRI) technique for non-invasive prenatal diagnostic approaches based on maternal blood analysis is confined. Here, we report a nanoparticle-enhanced SPRI strategy for a non-invasive prenatal fetal sex determination based on the detection of a Y-chromosome specific sequence (single-gene SRY) in cell-free fetal DNA from maternal plasma. The SPR assay proposed here allows for detection of male DNA in mixtures of 2.5 aM male and female genomic DNAs with no preliminary amplification of the DNA target sequence, thus establishing an analytical protocol that does not require costly, time-consuming, and prone to sample contamination PCR-based procedures. Afterward, the developed protocol was successfully applied to reveal male cell-free fetal DNA in the plasma of pregnant women at different gestational ages, including early gestational ages. This approach would pave the way for the establishment of faster and cost-effective non-invasive prenatal testing.

Cell-Free Fetal DNA Testing for Prenatal Diagnosis

Prenatal diagnosis and screening have undergone rapid development in recent years, with advances in molecular technology driving the change. Noninvasive prenatal testing (NIPT) for Down syndrome as a highly sensitive screening test is now available worldwide through the commercial sector with many countries moving toward implementation into their publically funded maternity systems. Noninvasive prenatal diagnosis (NIPD) can now be performed for definitive diagnosis of some recessive and X-linked conditions, rather than just paternally inherited dominant and de novo conditions. NIPD/T offers pregnant couples greater choice during their pregnancy as these safer methods avoid the risk of miscarriage associated with invasive testing. As the cost of sequencing falls and technology develops further, there may well be potential for whole exome and whole genome sequencing of the unborn fetus using cell-free DNA in the maternal plasma. How such assays can or should be implemented into the clinical setting remain an area of significant debate, but it is clear that the progress made to date for safer prenatal testing has been welcomed by expectant couples and their healthcare professionals.

Non-invasive prenatal diagnosis of trisomy 21 by dosage ratio of fetal chromosome-specific epigenetic markers in maternal plasma

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. Maternal 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 maternal 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.

Effective detection of fetal sex using circulating fetal DNA in first-trimester maternal plasma

The aim of this study was to develop a simple and effective method for noninvasively detecting fetal sex using circulating fetal DNA from first-trimester maternal plasma. A study was conducted with maternal plasma collected from 203 women between 5 and 12 wk of gestation. The presence of circulating fetal DNA was confirmed by a quantitative methylation-specific polymerase chain reaction of the unmethylated-PDE9A gene (U-PDE9A). Multiplex real-time PCR was used to simultaneously quantify the amount of DYS14 and GAPDH in maternal plasma. The results were confirmed by phenotype at birth. Pregnancy outcomes and U-PDE9A concentrations were obtained in all cases, including 99 male-bearing and 104 female-bearing participants. At equivalent specificity (100%), the false-negative rate was 9.1% for DYS14 quantification cycle, 7.1% for DYS14 concentration, and 0.0% for the concentration ratio of DYS14/GAPDH, respectively. In male-bearing participants, DYS14, U-PDE9A, and GAPDH concentrations were significantly lower in the false-negative case than in correct case (P<0.001 in all). Moreover, DYS14, U-PDE9A, and GAPDH concentrations showed significantly positive associations with each other (P≤0.001 in all). The ratio of DYS14/GAPDH in maternal plasma was an effective biomarker for noninvasive fetal sex detection during the first trimester, indicating that it could be useful for clinical application.