Non-Invasive Blood Test Enables Prenatal Genetic Screening for Fetal Conditions

Non-invasive prenatal testing (NIPT), which is also known as prenatal-cell-free DNA screening, refers to a blood test for pregnant individuals to screen for significant chromosomal changes like an extra chromosome 21 (Down syndrome), other chromosomal gains or losses, and the number of sex chromosomes. But for many prenatal genetic diagnoses, identifying individual nucleotide changes across the protein-coding sequence of the genome, known as the ‘exome’ is essential. Currently, exome screening requires invasive procedures like amniocentesis, which are costly and pose risks to both mother and fetus. Now, a non-invasive genetic test can screen the blood of pregnant individuals to survey all genes for fetal DNA sequence variants.

Developed by researchers at Massachusetts General Hospital (MGH, Boston, MA, USA), this new test uses a method termed non-invasive fetal sequencing (NIFS) to discover and interpret variants across the fetal exome from DNA circulating in the mother’s blood. The high-resolution NIFS approach method enables researchers to survey the exome, identify sequence changes, and distinguish potentially pathogenic variants from possibly benign variants inherited from the mother. The effectiveness of this test was demonstrated by the researchers through a blood sample analysis from 51 pregnant individuals. Using NIFS, maternal blood draw alone was sufficient, eliminating the need for additional genetic tests on either parent. The test managed to capture variants that were inherited from the mother as well as new variants that were not present in the mother and associated with prenatal diagnoses.

The test showed high sensitivity in identifying single-base DNA alterations and small insertions or deletions present in the fetal genome but absent in the maternal genome. This was consistent regardless of the fetal DNA amount detected. In 14 cases that underwent standard genetic testing, NIFS successfully detected all clinically relevant variants found in invasive testing. Although initially tested on 51 pregnancies, the potential for wider application exists. The research team is collaborating to broaden and validate these findings and enhance the methodology. It's crucial to note that this test isn't yet a clinical standard and requires further validation in larger samples. As research progresses, the team is also considering the best ways to support patients in navigating testing options and test results during pregnancy.

“Our study suggests that it is feasible to screen most genes across the fetal genome using a blood test rather than requiring an invasive procedure such as amniocentesis,” said senior author Michael E. Talkowski, PhD. “It has long been known that fetal sequence variants can be obtained from cell-free fetal DNA, and exome sequencing is already part of the standard-of-care, but it currently requires an invasive procedure.”

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