LETTERS TO THE EDITOR
Preimplantation Genetic Diagnosis and Screening To the Editor: I read with interest the recent SOGC technical update no. 323, Preimplantation Genetic Diagnosis and Screening.1 In the description of SNP microarray analysis, I took note of the statement: “In addition, SNP microarray can distinguish between balanced and normal chromosomes in embryos from a translocation carrier.” While this is true, it is important to highlight that SNP microarray is not applied for this purpose clinically. Treff et al.,2 the citation supporting the authors’ summary, is a case report, the study of a parent who has genetic syndrome (Alagille syndrome, ALGS1) and translocation between chromosomes 2 (q21) and 20 (p12.2). The translocation is considered balanced by karyotyping. Because of a recognized association between 20p12.2 breakpoints and the disruption of Jagged-1, a causative gene of ALGS1, the parent is suspected to have a microdeletion at that critical site. When SNP markers of Jagged-1 are evaluated and a microdeletion is diagnosed, the researchers have a tracking device for the so-called balanced translocation. Informative maternal and paternal SNPs help diagnose the derivative chromosome 20 in two cohorts of embryos. The purpose of Treff et al is “. . . to detect an inherited microdeletion associated with an apparently balanced translocation.” The intent is not the detection of embryos with balanced translocations, as the technical update seems to imply. Although we can count on continued research and broader applications of PGS technologies, in its current practical use, SNP microarray distinguishes only between abnormal and normal chromosome copy numbers. Ursula Durland, MS Certified Genetic Counsellor Pacific Centre for Reproductive Medicine
REFERENCES 1. Dahdouh EM, Balayla J, Audibert F; SOGC Genetics Committee. Preimplantation genetic diagnosis and screening. SOGC technical update no. 323, May 2015. J Obstet Gynaecol Can 2015;37(5):451–63.
686 l AUGUST JOGC AOÛT 2015
2. Treff NR, Tao X, Schillings WJ, Bergh PA, Scott RT Jr, Levy B. Use of single nucleotide polymorphism microarrays to distinguish between balanced and normal chromosomes in embryos from a translocation carrier. Fertil Steril 2011;96(1):e58–e65.
J Obstet Gynaecol Can 2015;37(8):686
In Response To the Editor: We thank Ursula Durland for her interest in our recent technical update on preimplantation diagnosis and screening (PGD/PGS), published in the May 2015 issue of the Journal of Obstetrics and Gynaecology Canada.1 Ms Durland seems to agree with our statement that “In addition, SNP microarray can distinguish between balanced and normal chromosomes in embryos from a translocation carrier,” but she calls for caution against its clinical use for that particular indication. It should be made clear that we do not claim that this platform should be systematically applied for the aforementioned indication. The cited reference by Treff et al.2 simply conveys that such application is technically feasible rather than clinically justified. The clinical indications for each cytogenetic technique are outlined in Table 2 of the technical update. Therefore, we concur with Ms Durland’s statement, and we thank her for pointing out this clarification as well as for her detailed explanations about the technical aspects of SNP microarray. The latter was not outlined in our publication as it is beyond the scope of the document, which is intended for use by the general community of obstetricians and gynaecologists in Canada. In our opinion, the sole purpose of introducing new genetic technologies into clinical practice is to improve clinical outcomes. This is mainly true for both aCGH and SNP microarray used in PGD cycles for couples carrying chromosomal rearrangements (e.g., translocations, microdeletions). With use of these technologies, by testing and selecting embryos with normal and complete chromosome copies for transfer, delivery rates can be improved. This is a major advantage when compared to the old FISH technology, which allows only a limited number of chromosomes to be tested. In this respect as well, we urge caution against inappropriate use of any new genetic technology, as was stated in the first two recommendations in our technical update, in which we call for an adequate
Preimplantation Genetic Diagnosis and Screening To the Editor: I read with interest the recent SOGC technical update no. 323, Preimplantation Genetic Diagnosis and Screening.1 In the description of SNP microarray analysis, I took note of the statement: “In addition, SNP microarray can distinguish between balanced and normal chromosomes in embryos from a translocation carrier.” While this is true, it is important to highlight that SNP microarray is not applied for this purpose clinically. Treff et al.,2 the citation supporting the authors’ summary, is a case report, the study of a parent who has genetic syndrome (Alagille syndrome, ALGS1) and translocation between chromosomes 2 (q21) and 20 (p12.2). The translocation is considered balanced by karyotyping. Because of a recognized association between 20p12.2 breakpoints and the disruption of Jagged-1, a causative gene of ALGS1, the parent is suspected to have a microdeletion at that critical site. When SNP markers of Jagged-1 are evaluated and a microdeletion is diagnosed, the researchers have a tracking device for the so-called balanced translocation. Informative maternal and paternal SNPs help diagnose the derivative chromosome 20 in two cohorts of embryos. The purpose of Treff et al is “. . . to detect an inherited microdeletion associated with an apparently balanced translocation.” The intent is not the detection of embryos with balanced translocations, as the technical update seems to imply. Although we can count on continued research and broader applications of PGS technologies, in its current practical use, SNP microarray distinguishes only between abnormal and normal chromosome copy numbers. Ursula Durland, MS Certified Genetic Counsellor Pacific Centre for Reproductive Medicine
REFERENCES 1. Dahdouh EM, Balayla J, Audibert F; SOGC Genetics Committee. Preimplantation genetic diagnosis and screening. SOGC technical update no. 323, May 2015. J Obstet Gynaecol Can 2015;37(5):451–63.
686 l AUGUST JOGC AOÛT 2015
2. Treff NR, Tao X, Schillings WJ, Bergh PA, Scott RT Jr, Levy B. Use of single nucleotide polymorphism microarrays to distinguish between balanced and normal chromosomes in embryos from a translocation carrier. Fertil Steril 2011;96(1):e58–e65.
J Obstet Gynaecol Can 2015;37(8):686
In Response To the Editor: We thank Ursula Durland for her interest in our recent technical update on preimplantation diagnosis and screening (PGD/PGS), published in the May 2015 issue of the Journal of Obstetrics and Gynaecology Canada.1 Ms Durland seems to agree with our statement that “In addition, SNP microarray can distinguish between balanced and normal chromosomes in embryos from a translocation carrier,” but she calls for caution against its clinical use for that particular indication. It should be made clear that we do not claim that this platform should be systematically applied for the aforementioned indication. The cited reference by Treff et al.2 simply conveys that such application is technically feasible rather than clinically justified. The clinical indications for each cytogenetic technique are outlined in Table 2 of the technical update. Therefore, we concur with Ms Durland’s statement, and we thank her for pointing out this clarification as well as for her detailed explanations about the technical aspects of SNP microarray. The latter was not outlined in our publication as it is beyond the scope of the document, which is intended for use by the general community of obstetricians and gynaecologists in Canada. In our opinion, the sole purpose of introducing new genetic technologies into clinical practice is to improve clinical outcomes. This is mainly true for both aCGH and SNP microarray used in PGD cycles for couples carrying chromosomal rearrangements (e.g., translocations, microdeletions). With use of these technologies, by testing and selecting embryos with normal and complete chromosome copies for transfer, delivery rates can be improved. This is a major advantage when compared to the old FISH technology, which allows only a limited number of chromosomes to be tested. In this respect as well, we urge caution against inappropriate use of any new genetic technology, as was stated in the first two recommendations in our technical update, in which we call for an adequate
