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Diagnosis of parental balanced reciprocal
translocations by trophectoderm biopsy
and comprehensive chromosomal
screening
Lian Liu, MD
Co-Authors:
L. W. Sundheimer1, L. Liu2 , R. P. Buyalos1,3 , G. Hubert1,3 , Z. Al-Safi1 , M.
Shamonki1,3
1 Division of Reproductive Endocrinology and Infertility, Department of
Obstetrics and Gynecology, David Geffen School of Medicine,
University of California, 10833 Le Conte Avenue, Room 27-139 CHS, Los
Angeles, CA 90095- 1740, USA
2 PacGenomics, 28222 Agoura Road Suite 200, Agoura Hills, CA 91301,
USA
3 Fertility and Surgical Associates of California, 325 Rolling Oaks Drive,
Thousand Oaks, CA 91361, USA
Abstract
Purpose This study investigates a case series of eight couples in one IVF center
who underwent trophectoderm (TE) biopsy and comprehensive chromosomal
screening (CCS) for routine aneuploidy screening and were found to have CCS
results concerning for previously undetected parental balanced reciprocal
translocations.
Methods In each case, controlled ovarian hyperstimulation and in vitro
fertilization (IVF) yielded multiple blastocysts that each underwent CCS with
high-density oligonucleotide microarray comparative genomic hybridization
(aCGH).
Results Parental translocations were suspected based on the finding of identical
breakpoint mutations in multiple embryos from each couple. Confirmation of
these suspected translocations within blastocysts was performed with next-
generation sequencing (NGS). Subsequent parental karyotypic evaluation
resulted in a diagnosis of parental balanced reciprocal translocation in each
case.
Conclusions We demonstrated that high-resolution aCGH and NGS on TE
biopsies can accurately detect parental reciprocal translocations when
previously unrecognized.
Typical log2 ratio charts for PGS from
PacGenomics
(Euploidy)
46, XX (vs. both Male and Female reference)
46, XY (vs. both Male and Female reference)
46, XX (vs. Male reference)
46, XY (vs. Male reference)
Array-based PGS NGS-based PGS
Typical log2 ratio charts for PGS
from PacGenomics
(Aneuploidy)
Array-based PGS NGS-based PGS
46, XY
Del of 3q22.2q29;
Dup of 5q12.1q35.3
46, XY
Del of 6q14.1q27;
Del of 13q12.11q14.11
Case one
Questions:
• What could be the diagnosis?
• Is it a 46, XY?
1
2
3
4
5
NGS-based PGS of the other samples from Case one
Combined view of all 5 samples’ Log2 ratios
Prediction of parental karyotype:
t(3;5),
the breakpoints at chr-3: 3q22.2
the breakpoints at chr-5: 5q12.1
Answer to Case one 46, XY
Yes. It is a 46, XY in a sense of “molecular” genetics.
But it also could be a balanced translocation if we examine it with cytogenetic method.
We recommended the patient couple for a blood karyotyping (G-banding). The
results was the mother has a balanced translocation between chr-3 and chr-5,
with the breakpoint as we predicted.
Case two
2
3
Questions:
• What could be the
diagnosis?
• Are they 46, XX and
46, XY?
1
7
6
5
4
3
2
Array-based PGS of the other samples from Case two
Prediction of parental karyotype:
t(6;13),
the breakpoints at chr-6: q14.1
the breakpoints at chr-13: q14.11
Combined view of all 7 samples’ Log2 ratios
Answer to Case two
46, XX
46, XY
But they also could be balanced
translocations if we examine them
with cytogenetic method.
We recommended the patient
couple for a blood karyotyping (G-
banding). The results was the
mother has a balanced
translocation between chr-6 and
chr-13, with the breakpoint as we
predicted.
2
3
What we did
All reported cases were identified based on judgment calls. An inherited translocation was suspected when
(1) at least two embryos of partial aneuploidy shared the exact same breakpoint(s);
(2) the breakpoint call log2 values were close to + 0.59 (gain)/− 1.0 (loss) to show no or very low mosaicism and signifying that the likely inherited translocation was most likely non-mosaic; or
(3) multiple embryos shared the same whole chromosome loss/gain.
Once the laboratory identified a suspected translocation, the referring provider was notified for further parent evaluation.
Summary Eight patient couples from the study cohort were identified as having a recurring
identical breakpoint mutation in their embryos via CCS, raising suspicion for a parental balanced translocation.
A total of 1847 CCS cases (in this IVF center, 2013~2016) were performed during the same time period, excluding previously known translocation cases, indicating an incidence of just over 0.4% of cases undergoing PGS for routine aneuploidy screening. The patients ranged in age from 28 to 38 years and male partners from 35 to 39 years. Patients elected for CCS and had a history of infertility or RPL (Table 1). A translocation was suspected when a segmental abnormality was detected with the identical chromosomal breakpoint mutation in more than one embryo. Of these cases, a total of 87 embryos were evaluated from 14 IVF cycles. Twenty distinct breakpoint mutations were identified. When a recurring breakpoint mutation was identified suggestive of a translocation, NGS testing was performed to replicate and validate the aCGH findings. In all cases, the high-density oligonucleotide aCGH and NGS results were identical.
None of the patients had a known history of translocation of POC, blood or any types. PGS has been the first sign the patient couple could be balanced translocation carriers.
The presence of a parental balanced reciprocal translocation was confirmed in one parent in all cases.
In one case (patient 2), a conventional karyotype had been performed prior to IVF and was reported as normal in both the male and female. After the CCS results for this couple were reviewed, the karyotypes were repeated with special attention to the breakpoint noted in the embryos. The resultant karyotype, 46, XX t(5:17)(q32;q23), confirmed the female patient as a translocation carrier.
Discussion
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Potential Clinical Applications
For balanced translocation carrier, we can use this to identify the reason for
infertility / multiple miscarriage.
If the patients (otherwise non-significant) have long history of infertility /
multiple miscarriage (the reason to seek IVF treatment), after parental
translocation be identified, sperm/oocyte donation may be
recommended.
For IVF patient who use sperm/oocytes donations, we can potentially
identify if the translocation inherited from the donor.