Faculty Bibliography

BACKGROUND:Cell-free DNA (cfDNA) non-invasive prenatal screening for trisomy (T) 21, 18, and 13 has been rapidly adopted into clinical practice. However, prior studies are limited by lack of follow up genetic testing to confirm outcomes and accurately assess test performance, particularly in women at low-risk for aneuploidy. OBJECTIVE:To compare the performance of cfDNA screening for T21, T18 and T13 between women at low and high-risk for aneuploidy in a large, prospective cohort with genetic confirmation of results. STUDY DESIGN/METHODS:A multicenter prospective observational study at 21 centers in 6 countries. Women who had SNP-based cfDNA screening for T21, T18 and T13 were enrolled. Genetic confirmation was obtained from prenatal or newborn DNA samples. Test performance and test failure (no-call) rates were assessed for the cohort and women with low and high prior risk for aneuploidy were compared. An updated cfDNA algorithm, blinded to pregnancy outcome, was also assessed. RESULTS:20,194 were enrolled at median gestational age of 12.6 weeks (IQR:11.6, 13.9). Genetic outcomes were confirmed in 17,851 (88.4%): 13,043 (73.1%) low-risk and 4,808 (26.9%) high-risk for aneuploidy. Overall, 133 trisomies were diagnosed (100 T21; 18 T18; 15 T13). cfDNA screen positive rate was lower in low- vs. high-risk (0.27% vs. 2.2%, p<0.0001). Sensitivity and specificity were similar between groups. The positive predictive value (PPV) for the low and high-risk groups was 85.7% vs. 97.5%, p=0.058 for T21; 50.0% vs. 81.3%, p=0.283 for T18; and 62.5% vs. 83.3, p=0.58 for T13, respectively. Overall, 602 (3.4%) patients had no-call result after the first draw and 287 (1.61%) after including cases with a second draw. Trisomy rate was higher in the 287 with no-call results than patients with a result on a first draw (2.8% vs. 0.7%, p=0.001). The updated algorithm showed similar sensitivity and specificity to the study algorhitm with a lower no-call rate. CONCLUSIONS:In women at low-risk for aneuploidy, SNP-based cfDNA has high sensitivity and specificity, PPV of 85.7% for T21 and 74.3% for the three common trisomies. Patients who receive a no-call result are at increased risk of aneuploidy and require additional investigation.

Epigenetics refers to structural modifications to genes that do not change the nucleotide sequence itself but instead control and regulate gene expression. DNA methylation, histone modification, and RNA regulation are some of the mechanisms involved in epigenetic modification. Epigenetic changes are believed to be a result of changes in an organism's environment that result in fixed and permanent changes in most differentiated cells. Some environmental changes that have been linked to epigenetic changes include starvation, folic acid, and various chemical exposures. There are periods in an organism's life cycle in which the organism is particularly susceptible to epigenetic influences; these include fertilization, gametogenesis, and early embryo development. These are also windows of opportunity for interventions during the reproductive life cycle of women to improve maternal-child health. New data suggest that epigenetic influences might be involved in the regulation of fetal development and the pathophysiology of adult diseases such as cancer, diabetes, obesity, and neurodevelopmental disorders. Various epigenetic mechanisms may also be involved in the pathogenesis of preeclampsia and intrauterine growth restriction. Additionally, environmental exposures are being held responsible for causing epigenetic changes that lead to a disease process. Exposure to heavy metals, bioflavonoids, and endocrine disruptors, such as bisphenol A and phthalates, has been shown to affect the epigenetic memory of an organism. Their long-term effects are unclear at this point, but many ongoing studies are attempting to elucidate the pathophysiological effects of such gene-environment interactions