Prenatal genetic screening to expand
A new form of pre-natal genetic screening may be able to predict future ailments using only a sample of the mother’s blood. Scientists led by Stephen Quake of Stanford University published their findings on July 4 in Nature journal. The findings were released a month after another technique was announced by scientists led by Jay Shendure of the University of Washington that could sequence the fetus’ genome using the mother’s and the father’s blood. The new test would cut down on error due to uncertainty of who fathered the child. The procedure is also noninvasive and does not have a risk of miscarriage, unlike amniocentesis and chorionic villus sampling.
The test works by sequencing the fetal genome using millions of DNA fragments in the mother’s blood. During the early stages of pregnancy, 5 to 10 per cent of the fragments come from the unborn child. There is no direct way to distinguish the fetal from the maternal DNA. Instead, investigators measured the proportions of different DNA variants, reasoning that the most common variants came from the mom and the least common from the child.
The scientists admitted, however, that the study was proof of principle and may not work outside of the lab. Gene sequences were only determined for two fetuses – one came from a healthy mother and the other from a mother who had DiGeorge syndrome, which causes cardiac, muscular, and cognitive problems. The test accurately predicted that her child will have DiGeorge syndrome too.
Stephen Quake argued that although knowing the fetal genome could encourage women to abort, it could also permit immediate treatment, including through prenatal surgery. “Now we can challenge our colleagues in surgery and pharmacology,” said Quake. “We’ll soon be able to diagnose all these genetic disorders; what are you going to do about them?”
Advocates of pre-natal screening insist that it would also give parents time to prepare for a child with special needs. The authors mention phenylketonurea and maple syrup urine disease (which affect the metabolism of certain amino acids) as possible genetic disorders that could be tracked and their harmful effects mitigated by imposing a special diet on the patient. In all, Reuters reports that there are about 3,000 possible genetic disorders that theoretically could be identified.
In reality, though, the picture looks much darker. According to the National Down Syndrome Cytogenetic Register in the United Kingdom, from 1989 to 2006, 92 per cent of mothers aborted their children after discovering through prenatal testing that they would have Down’s syndrome. Both Down’s syndrome and DiGeorge syndrome have no cure.
These genetic tests are not completely accurate – it misses some mutations and mistakes some healthy genes for abnormal ones. There is always a chance for false positives and parents terminating the life of a healthy preborn baby.
The new procedure has also raised ethical questions. “Do we tell the pregnant woman about serious, moderate, or mild diseases?” asks Stanford bioethicist Hank Greely. “About hair color, eye color? About Alzheimer’s risks for 70 years later? About the hundreds of variants of unknown significance found in every genome?”
Pro-life bioethics blogger Rebecca Taylor did not welcome the news of broader prental genetic screening. She wrote, “because we live in a society where abortion on demand is prevalent, this is terrible news. The information provided with this technique will likely lead to more abortions for ever more trivial traits.”