Down's syndrome in fetuses can now be detected through the use of a blood test that detects markers in DNA. The new technique is believed to be more accurate than conventional methods at detecting the disorder.
The blood test is administered between 10 and 14 weeks of pregnancy.
University of California San Francisco researchers reveal that two other chromosomal abnormalities, more rare than Down's syndrome, can also be detected through the same test.
The study examined results from 16,000 pregnant women, and the technique successfully detected Down's syndrome in all 38 cases where the abnormality was present. The new test also produced nine false positives, significantly better than the 854 detected using traditional screening methods.
Physical examinations of the newborns as well as genetic testing were carried out to confirm the diagnoses in these babies. Women in the study averaged 30 years old, and 25 percent were past the age of 35. This is the age at which women are generally considered to be at high risk of complications from pregnancy, causing physicians to carry out additional tests, such as amniocentesis.
The test isolates a small concentration of fetal DNA present in the bloodstreams of women carrying offspring. These molecules are subjected to a polymerase chain reaction, producing copies of the DNA, which allows for analysis of the genetic material.
Down's syndrome results in a multitude of medical disorders, including cognitive impairment. The disorder results from an extra copy of chromosome 21. Humans have 23 sets of chromosomes that determine physical characteristics, and some mutations can also result in illness or disorders.
An ultrasound of the fetus can also be performed during examinations, searching for excess nuchal fold fluid at the back of the neck, which is indicative of the disorder.
Edward's Syndrome, also known as trisome 18, and Patau Sydrome, trisomy 13, can also be detected using this new technique. Down's syndrome accounts for roughly half the cases of disorders driven by abnormal numbers of chromosomes, known as aneuploidies. Standard screening techniques may be better than the new blood test at detecting these disorders, researchers state.
"Providers need to be attuned to patients' preferences and counsel them about the differences in prenatal screening and diagnostic testing options. Those women who do opt for cell-free DNA testing should be informed that it is highly accurate for Down syndrome, but it focuses on a small number of chromosomal abnormalities and does not provide the comprehensive assessment available with other approaches," Mary Norton of UCSF said.
Although the new test is highly accurate at detecting Down's syndrome, it is unable to detect many disorders which show up on standard tests.
Development of the new genetic testing technique was published in the New England Journal of Medicine.
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