Full Prenatal Genetic Testing May Diagnose Rare Diseases

Screening all chromosomes could identify additional prenatal abnormalities.

Non-invasive prenatal screening for all 24 chromosomes may uncover genetic disorders that result in miscarriage and abnormal pregnancies, according to a new study published by Science Translational Medicine.

Typically, genetic tests performed during pregnancy search for duplicate copies of chromosomes 21, 18, and 13. While full genomic testing is rare, the authors hypothesize that it may improve the accuracy of prenatal tests.

Mothers often request non-invasive genetic screening, but the tests normally check for Down Syndrome and other common trisomies, which occur when there are 3 sets of chromosomes, according to the study.

“Extending our analysis to all chromosomes allowed us to identify risk for serious complications and potentially reduce false-positive results for Down syndrome and other genetic conditions,” said senior study author Diana W. Bianchi, MD, chief of the Prenatal Genomics and Therapy Section at NIH’s National Human Genome Research Institute.

In the study, the authors sequenced DNA from nearly 90,000 samples of maternal plasma from American and Australian women. The researchers determined the normalized chromosome denominator quality (NCDQ). The NCDQ measures the chance a sample has 2 chromosomes. Patients with an NCDQ of 50 or lower were analyzed further, according to the authors.

Among the samples from the American cohort, 0.45% were analyzed further and classified as abnormal, while 0.42% of samples from the Australian cohort were classified as abnormal, with a majority containing a trisomy, according to the study.

The authors noted that trisomy 7 was the most common among all study participants, followed by trisomies 15, 16, and 22.

Pregnancy and outcomes data were available for nearly all cases of the rare trisomies detected in the Australian cohort.

The authors found that 22 samples resulted in early miscarriages before 12 weeks of gestations, including samples with trisomy 15 and 22, according to the study.

These findings suggest that more inclusive genetic testing may give a better picture of genetic abnormalities prior to birth.

“We found that pregnancies at greatest risk of serious complications were those with very high levels of abnormal cells in the placenta,” said co-first author of the study Mark D. Pertile, PhD, head of the division of reproductive genetics at Victorian Clinical Genetics Services, part of Murdoch Children’s Research Institute in Melbourne, Australia. “Our results suggest that patients be given the option of receiving test results from all 24 chromosomes.”