The challenges of applying genome-wide technologies to prenatal testing in Canadian medical practice was discussed in a symposium at University of Toronto's McLaughlin Center. The report was published in a recent issue of Journal of Medical Genetics.
The symposium was attended by 59 clinical or laboratory geneticists, genetic counsellors, and maternal fetal medicine specialists from 17 centers in 8 provinces of Canada. Also present were ethicist Dr. Kerry Bowman, geneticists Drs. Bettina Blaumeiser (Belgium) and Bronwyn Kerr (UK). Several speakers shared their experiences and opinions in the symposium. Health care in Canada is regulated by provincial jurisdiction. Policies and choices regarding health services are made and implemented by respective provincial and territorial Ministries of Health. This results in discrepancies between provinces in several health services including genetics. Some national bodies like The Canadian College of Medical Geneticists (CCMG) and Canadian Association of Genetic Counselors (CAGC), along with Society of Obstetricians and Gynecologists of Canada (SOGC) put in place policy and practice guidelines, to be considered by individual provinces and centers.
AdvertisementGenomic microarrays have become important for the diagnosis of several chromosomal abnormalities postnatally, that is, after the baby is born. The symposium focused on genomic assays (microarrays and sequencing) that can be done prenatally, that is before the baby is born. These can be carried out on fetal DNA obtained from amniotic fluid, chorionic villus sampling or probably even from maternal circulation. In a microarray, several genes are examined simultaneously.
Some of the topics of discussion where a consensus was reached in the symposium included the following:
- Availability and Access to Testing: According to the group, a microarray can be offered for specific abnormal ultrasound findings or increased nuchal translucency. If microarray is offered, it should be a publicly funded service and should include pre- and post-test counseling. G-banded karyotype, another genetic test, is needed for follow-up to determine imbalance mechanism, confirm changes in chromosome numbers, if microarray fails, or for family history suggesting chromosome rearrangement.
- Counseling and Education: Tools developed to assist counseling and consenting could be shared among centers. Tools like pre-counseling videos can save counseling time and also facilitate in decision making.
- Genomic Technologies and Result Reporting: Prenatal array should have the same resolution as used for postnatal analyses. With reference to reporting of results, any medically actionable findings should be reported. Recessive carrier status when carrier frequency is >1/50 and other testing is available should also be reported. A carrier is a person who has a genetic problem but does not suffer from the condition. However, there is a possibility that he/she can pass it on to the next generation. A multi-disciplinary ad hoc committee should be set up to provide guidance on several other issues.
- Future Considerations: The group predicted that in the first trimester, non-invasive testing would replace biochemical screening for all pregnant women in a period of around 5 to 10 years. In the non-invasive testing, fetal DNA from the mother's blood are obtained for testing.
References:Buchanan JA, Chitayat D, Kolomietz E, Lee HC, Scherer SW, Speevak MD, Sroka H, Stavropoulos DJ. Prenatal genomic microarray and sequencing in Canadian medical practice: towards consensus. J Med Genet.2015. 1-10