Fishing for DNA

One of the most promising prenatal diagnostic tests in the works might one day eliminate altogether the need for amniocentesis or chorionic villus sampling. Its strategy: testing the mother’s blood for fetal DNA. For years, Diana Bianchi, a neonatologist and medical geneticist at the Tufts-New England Medical Center in Boston, and others had hoped that fetal cells found in maternal blood might provide a noninvasive means for assessing a baby’s genetic makeup. But, Bianchi explains, the cells proved too few in number and thus too difficult to find. In 1997 a team led by Dennis Lo of the Chinese University of Hong Kong first reported the discovery of fetal DNA floating freely in maternal serum and plasma. Since then, preliminary evidence from Bianchi’s group and other researchers has shown that this fetal DNA can be assessed for chromosomal or gene defects.

As ever more information pours out about the relationship between genes and diseases, and as screening tools become more sophisticated, prospective parents will inevitably face harder decisions about the types of babies they want to bring into the world. New tools such as DNA microarrays could soon enter the arena of preimplantation and prenatal genetic diagnosis, allowing physicians to screen DNA for a host of genetic diseases simultaneously.

Prenatal screens and diagnostics cannot eliminate all of the uncertainties about the health of a newborn. They can dramatically reduce them, though, and that is the aim of the technologies. But the same diagnostics also raise vexing ethical questions. As the technology continues to advance, parents will gain the ability to determine whether their offspring have genes that “predispose” them to diseases such as Alzheimer’s or breast cancer. In the end, these future tests could themselves introduce ethical ambiguities that no amount of science and technology can overcome.

Genetic Diagnostic Tools