FERTILITY GENETICS

ARTICLES
next generation sequencing (NGS) (Wells et al. 2014).
aCGH is particularly robust and was the first technique to
be widely available for reliable copy number analysis of
all chromosomes with a short turnaround time. Multiple
randomized clinical trials have validated these methods
and provided strong evidence that aneuploidy screening
through PGS can be translated into a better clinical outcome
(Schoolcraft and Katz-Jaffe 2013; Scott et al. 2013; Yang et al.
2012).
Particularly exciting is the implementation of NGS to the
PGD/PGS field. NGS involves fragmenting genomic DNA
from the biopsied cells, followed by parallel sequencing
until a sufficient number of reads is achieved. This level of
coverage will determine the application of NGS. Low depth
of genomic coverage has been shown to be sufficient for
aneuploidy detection (Fan et al. 2015; Fiorentino et al. 2014;
Wells et al. 2014; Yin et al. 2013). Deeper sequencing offers the
possibility of a more powerful and comprehensive analysis,
which can lead to the detection of single-gene defects (Treff
et al. 2013). Although some technical limitations remain,
due to rapidly evolving sequencing technologies and
declining costs, NGS of the entire embryo genome might
become a reality of the clinical practice in coming years.
This will unavoidably raise ethical questions and pose
challenges for data interpretation and patient counseling.
Nevertheless, it will provide an unprecedented amount of
information that will help geneticists and clinicians gain a
deeper understanding of the biology of the embryo.
Although the development of accurate non-invasive
methods for assessing embryo aneuploidy is desirable,
PGD-PGS remains the only reliable approach to guarantee
the transfer of a chromosomally normal and unaffected
embryo. Continuous advances in genetic testing open up
exciting venues for the future and the implementation of
cost-effective, highly-accurate diagnostic methods hold
the potential to have profound implications in the way
embryo normalcy is determined, to strengthen the position
of PGD in IVF cycles, and to ultimately benefit patients and
treatment success rates.
References
Fan, J., et al. (2015), ‘The clinical utility of next-generation
sequencing for identifying chromosome disease syndromes
in human embryos’, Reprod Biomed Online, 31 (1), 62-70.
Fiorentino, F., et al. (2014), ‘Application of next-generation
sequencing technology for comprehensive aneuploidy
screening of blastocysts in clinical preimplantation genetic
screening cycles’, Hum Reprod, 29 (12), 2802-13.
Fiorentino, F., et al. (2004), ‘Development and clinical application
of a strategy for preimplantation genetic diagnosis of single
gene disorders combined with HLA matching’, Mol Hum
Reprod, 10 (6), 445-60.
Gutierrez-Mateo, C., et al. (2011), ‘Validation of microarray
comparative genomic hybridization for comprehensive
chromosome analysis of embryos’, Fertil Steril, 95 (3), 953-8.
Handyside, A. H. (2013), ‘24-chromosome copy number analysis:
a comparison of available technologies’, Fertil Steril, 100 (3),
595-602.
Handyside, A. H., et al. (1990), ‘Pregnancies from biopsied
human preimplantation embryos sexed by Y-specific DNA
amplification’, Nature, 344 (6268), 768-70.
Handyside, A. H., et al. (2010), ‘Karyomapping: a universal
method for genome wide analysis of genetic disease based
on mapping crossovers between parental haplotypes’, J Med
Genet, 47 (10), 651-8.
Harton, G. L., et al. (2011), ‘ESHRE PGD consortium best practice
guidelines for amplification-based PGD’, Hum Reprod, 26 (1),
33-40.
Konstantinidis, M., et al. (2015), ‘Live births following
Karyomapping of human blastocysts: experience from
clinical application of the method’, Reprod Biomed Online, 31
(3), 394-403.
Mastenbroek, S., et al. (2011), ‘Preimplantation genetic screening:
a systematic review and meta-analysis of RCTs’, Hum Reprod
Update, 17 (4), 454-66.
Morales, C., et al. (2008), ‘Cytogenetic study of spontaneous
abortions using semi-direct analysis of chorionic villi samples
detects the broadest spectrum of chromosome abnormalities’,
Am J Med Genet A, 146A (1), 66-70.
Munne, S., et al. (1993a), ‘A fast and efficient method for
simultaneous X and Y in situ hybridization of human
blastomeres’, J Assist Reprod Genet, 10 (1), 82-90.
Munne, S., et al. (1993b), ‘Diagnosis of major chromosome
aneuploidies in human preimplantation embryos’, Hum
Reprod, 8 (12), 2185-91.
Natesan, S. A., et al. (2014), ‘Live birth after PGD with
confirmation by a comprehensive approach (karyomapping)
for simultaneous detection of monogenic and chromosomal
disorders’, Reprod Biomed Online, 29 (5), 600-5.
Schoolcraft, W. B. and Katz-Jaffe, M. G. (2013), ‘Comprehensive
chromosome screening of trophectoderm with vitrification
facilitates elective single-embryo transfer for infertile women
with advanced maternal age’, Fertil Steril, 100 (3), 615-9.
Scott, R. T., Jr., et al. (2013), ‘Blastocyst biopsy with comprehensive
chromosome screening and fresh embryo transfer significantly
increases in vitro fertilization implantation and delivery rates:
a randomized controlled trial’, Fertil Steril, 100 (3), 697-703.
Thornhill, A. R., et al. (2015), ‘Karyomapping-a comprehensive
means of simultaneous monogenic and cytogenetic PGD:
comparison with standard approaches in real time for Marfan
syndrome’, J Assist Reprod Genet, 32 (3), 347-56.
Treff, N. R., et al. (2010), ‘Accurate single cell 24 chromosome
aneuploidy screening using whole genome amplification and
single nucleotide polymorphism microarrays’, Fertil Steril, 94
(6), 2017-21.
Treff, N. R., et al. (2012), ‘Development and validation of an accurate
quantitative real-time polymerase chain reaction-based
assay for human blastocyst comprehensive chromosomal
aneuploidy screening’, Fertil Steril, 97 (4), 819-24.
Treff, N. R., et al. (2013), ‘Evaluation of targeted next-generation
sequencing-based preimplantation genetic diagnosis of
monogenic disease’, Fertil Steril, 99 (5), 1377-84 e6.
Wells, D., et al. (2014), ‘Clinical utilisation of a rapid low-pass
whole genome sequencing technique for the diagnosis of
aneuploidy in human embryos prior to implantation’, J Med
Genet, 51 (8), 553-62.
Yang, Z., et al. (2012), ‘Selection of single blastocysts for fresh
transfer via standard morphology assessment alone and with
array CGH for good prognosis IVF patients: results from a
randomized pilot study’, Mol Cytogenet, 5 (1), 24.
Yin, X., et al. (2013), ‘Massively parallel sequencing for
chromosomal abnormality testing in trophectoderm cells of
human blastocysts’, Biol Reprod, 88 (3), 69.
Fertility Genetics Magazine • Volume 2 • www.FertMag.com – Page 35