New and Emerging Technologies in the Diagnosis of Genetic Diseases

Posted by The Evidence Blog on October 23, 2012

By Diane Allingham-Hawkins, PhD, FCCMG, FACMG, Director of the Hayes Genetic Test Evaluation Program

The final day of the 36th Annual Scientific Meeting of the Canadian College of Medical Geneticists (CCMG) addressed new and emerging technologies in the diagnosis of genetic diseases. The morning session was devoted to the use of these technologies in prenatal diagnosis. Dr. David Chitayat of the University of Toronto provided a comprehensive overview of the current options for the prevention, diagnosis, and treatment of fetal disorders. Dr. Sylvie Langlois discussed the newly developed noninvasive methods of screening pregnancies for Down syndrome and other numerical chromosome anomalies in the fetus using fetal DNA circulating in the maternal serum. These tests, which currently cost $800 to $1800 each, have emerged in the last 6 to 12 months and are designed as an alternative screening modality for pregnant women. Women who screen positive by one of these so-called noninvasive prenatal tests (NIPD) would need an invasive procedure such as amniocentesis or chorionic villus sampling to confirm the diagnosis. Dr. Langlois indicated that although these tests are likely not sufficiently validated for first-line use in all pregnant women, they may be useful in high-risk pregnancies detected by a biochemical screening test or another test such as ultrasound. Hayes has evaluated the three major versions of these tests that are currently marketed in the United States. We found that currently there is insufficient evidence to determine their usefulness in the care of pregnant women.

Dr. Lisa Shaffer, formerly of Signature Genomics, discussed Signature Genomics’ experience with the use of chromosomal microarrays in the prenatal setting. Reporting on the results of more than 5000 cases, Dr. Shaffer indicated that 5.4% of cases with a normal karyotype will have a clinically significant change identified on microarray. However, variants of unknown clinical significance will also be identified in 4.2% of cases, which presents a genetic counselling dilemma in the prenatal population. The data suggest that abnormal results are more likely when abnormalities are seen in two or more organ systems by ultrasound (> 9%), indicating that it may be prudent to stratify patients by risk prior to performing microarray in the prenatal setting. Dr. Shaffer emphasized that the benefit of prenatal microarray testing must outweigh the risk of unclear results.

A panel discussion ended the session with emphasis on the need for comprehensive genetic counselling of patients prior to the use of any prenatal technology in order to minimize the potential for harm.

In the first session of the afternoon, Dr. Kim Boycott of the University of Ottawa reported on the Finding of Rare Disease Genes in Canada (FORGE Canada) project, an ambitious project to identify the genetic basis of 200 rare diseases in Canadian patients using whole-exome sequencing. Dr. Boycott reported that 77 different genes have been identified in 132 disorders to date and that 36 of the genes identified were novel (previously unknown) genes.

The final scientific session of the meeting focused on specific genetic diagnostic challenges in Saskatchewan. Dr. Ali Rajput and Dr. Peter Hull of the University of Saskatchewan reported on their work identifying disease genes in Parkinson’s disease and dermatologic disorders, respectively. Dr. Denis Lehotay, also of the University of Saskatchewan, provided an overview of newborn screening in Saskatchewan. Dr. James Irvine, the Medical Health Officer for three northern Saskatchewan health authorities, closed the meeting with an excellent discussion of the unique considerations when performing research in aboriginal populations.

Topics: Hayes Blog, Genetic Testing

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