Taryn Charles, Public Health Genetics
Many people these days complain of feeling overwhelmed by information. But for pregnant women having prenatal testing, it’s a very real situation.
Chorionic villus sampling and amniocentesis are two ways of collecting samples from a developing baby to test for genetic abnormalities such as Down syndrome and cystic fibrosis. Both are invasive procedures and involve the use of a needle to take a placenta sample, in the case of chorionic villus sampling, and a small amount of amniotic fluid from around the baby in amniocentesis.
To analyse these samples, a karyotype is usually performed. A karyotype is like a photograph of the developing baby’s chromosomes. It allows scientists to see if there are any extra, missing or rearranged chromosomes.
While the karyotype has been the gold standard in testing, there is a new method now being used called a chromosome microarray. A microarray is like a zoom lens on a camera, allowing scientists to see DNA in much greater detail. Microarrays can identify changes in the DNA called copy number variants. As the name suggests, these are variants in the amount of DNA – either extra or missing pieces – but viewed at a much higher resolution than in the chromosome photographs.
Some of these copy number variants are known by scientists already and their effect on the health of the future baby is well understood. But for others, it’s not so clear. There are ‘normal/benign’ variants, which do not affect health and development, and there are ‘pathogenic’ variants, which are known to cause health problems such as intellectual disability and delays in development. Unfortunately, there are also copy number variants of ‘unknown and uncertain’ nature.
Unknown variants are those that are new and have not been seen before in other people – their effect on health is unclear. Uncertain copy number variants have been seen in the DNA before, but their effect on health is ‘uncertain’. That is, it can’t be predicted, and may range from mild to severe. The difficulty with these copy number variants found during pregnancy is that there is no way of knowing what the outcome will be for the future child.
So if a pregnant woman and her partner receive a microarray result that shows an unknown or uncertain copy number variant has been identified, what are they to do with that information?
Researchers in the United States have found that receiving such ‘unknown and uncertain’ results presents challenges when it comes to prenatal decision making. Some women considered the information to be ‘toxic knowledge’, or information they wish they didn’t have. Many began a process of desperately searching for information that would help them make informed decisions, but such information simply doesn’t exist.
Currently, in Australia, there are no guidelines or policies in terms of what to report from prenatal microarray tests, and no one has consulted with women locally to find out their thoughts. So, the Murdoch Children's Research Institute has launched the Genomics and Pregnancy, or GaP study.
This study aims to offer women having a prenatal microarray a choice about the type of information they want to receive. They can opt for ‘targeted’ information, where only the known copy number variants will be reported. Or they can choose ‘extended’ information, where all copy number variants, disease-associated, unknown and uncertain, are reported. The study aims to look at the number of women choosing each type of information option, and also look at their decision-making process and how they deal with uncertainty. A GaP decision aid has been developed to help study participants consider the options.
The ultimate goal is that findings from this study will be used to inform the development of relevant policy for the reporting of prenatal microarray results. The study will provide a vital evidence base for other genetic technologies, where our ability to identify DNA changes is outpacing our level of understanding about what they mean.
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