Down Syndrome

New DNA test more accurate detecting Down Syndrome in pregnancy

It was the news Jennifer Fontaine had been dreading: Her unborn child tested positive for a deadly chromosome abnormality. “When I got a positive result, it was very devastating,” said Fontaine.

Her then unborn daughter had tested positive for trisomy 18, a deadly chromosome abnormality. Half of infants don’t survive their first week of life, according to the National Institutes of Health.

“I researched online, and the things I was seeing, it was very upsetting,” said Fontaine.

“Women (like Fontaine) are being given troubling news or anxiety provoking news,” said Dr. Diana Bianchi, a medical geneticist and executive director of the Mother Infant Research Institute at Tufts Medical Center.

What’s even worse is that that news is often wrong.

“Ninety-six percent of the time the screening test was positive, but the fetus has normal chromosomes,” said Bianchi.

But a new screening test is promising to cut down on false positives. It’s a simple blood draw called a cell-free DNA test, where doctors analyze fetal DNA circulating in the mother’s blood. In today’s New England Journal of Medicine, researchers at Tufts Medical Center compared the DNA test to current screening methods with stunning results

“Only 3 percent of the women had a false positive result. But if you had a positive result, then there was a 45 percent chance that the fetus actually had Down syndrome,” said Bianchi.

According to the study, the new DNA test is 10 times more accurate than standard tests and safer, too.

“Fewer women are going on to have unnecessary invasive diagnostic tests (like amniocentesis),” said Bianchi.

In amniocentesis, a needle is injected directly into the womb.

“There is a small chance of miscarriage associated with amniocentesis,” said Bianchi.

Less than a week after her DNA screening test, Fontaine’s doctors gave her the good news.

“The results were negative … she was perfect. Her DNA was perfect. The chromosomes were fine,” said Fontaine. “We were ecstatic.”

On Dec. 17, 2013, Morgan Stephanie was born. She weighed 6 pounds and 4 ounces and was 100 percent healthy.

“She’s doing great. She’s hitting all of her milestones,” said Fontaine.

The DNA test is already available for high-risk pregnancies, but currently, insurance doesn’t cover it in low risk women. Bianchi said that may soon change as more studies come out confirming Tufts’ findings.

source: wcvb

FDA approves post-natal test to help diagnose developmental delays

The US Food and Drug Administration has authorized for marketing the Affymetrix CytoScan Dx Assay, which can detect chromosomal variations that may be responsible for a child’s developmental delay or intellectual disability. Based on a blood sample, the test can analyse the entire genome at one time and detect large and small chromosomal changes.

According to the National Institutes of Health and the American Academy of Paediatrics, two to three per cent of children in the United States have some form of intellectual disability. Many intellectual and developmental disabilities, such as Down syndrome and DiGeorge syndrome, are associated with chromosomal variations.

“This new tool may help in the identification of possible causes of a child’s developmental delay or intellectual disability, allowing healthcare providers and parents to intervene with appropriate care and support for the child,” said Alberto Gutierrez, director of the Office of In Vitro Diagnostics and Radiological Health in the FDA’s Centre for Devices and Radiological Health. “The FDA’s review of the test provides clinical laboratories with information about the expected performance of the device and the quality of the results.”

The FDA reviewed the Affymetrix CytoScan Dx Assay through its de novo classification process, a regulatory pathway for some novel low-moderate-risk medical devices.

For the de novo petition, the FDA’s review of the CytoScan Dx Assay included an analytical evaluation of the test’s ability to accurately detect numerous chromosomal variations of different types, sizes, and genome locations when compared to several analytically validated test methods. The FDA found that the CytoScan Dx Assay could analyse a patient’s entire genome and adequately detect chromosome variations in regions of the genome associated with intellectual and developmental disabilities.

Additionally, the agency’s review included a study that compared the performance of the CytoScan Dx Assay to tests that are commonly used for detecting chromosomal variations associated with a developmental delay or intellectual disability. A comparison of test results from 960 blood specimens showed the CytoScan Dx had improved ability over commonly used tests, including karyotyping and FISH chromosomal tests, to detect certain chromosomal abnormalities.

This device should not be used for stand-alone diagnostic purposes, pre-implantation or prenatal testing or screening, population screening, or for the detection of, or screening for acquired or genetic aberrations occurring after birth, such as cancer. The test results should only be used in conjunction with other clinical and diagnostic findings, consistent with professional standards of practice, including confirmation by alternative methods, evaluation of parental samples, clinical genetic evaluation, and counselling as appropriate, according to a statement issued by the FDA.

Interpretation of test results is intended to be performed only by healthcare professionals who are board certified in clinical cytogenetics or molecular genetics, the statement said.

Affymetrix CytoScan Dx Assay is manufactured by Affymetrix, Inc, located in Santa Clara, California.

Source: India Medical Times