Reproductive risks and preimplantation genetic testing intervention for X-autosome translocation carriers

RESEARCH QUESTION

What is the genetic cause of multiple congenital disabilities in a girl with a maternal balanced X-autosome translocation [t(X-A)]? Is preimplantation genetic testing (PGT), to distinguish non-carrier from euploid/balanced embryos and prioritize transfer, an effective and applicable strategy for couples with t(X-A)?

DESIGN

Karyotype analysis, whole-exome sequencing and X inactivation analysis were performed for a girl with congenital cardiac anomalies, language impairment and mild neurodevelopmental delay. PGT based on next-generation sequencing after microdissecting junction region (MicroSeq) to distinguish non-carrier and carrier embryos was used in three couples with a female t(X-A) carrier (cases 1-3).

RESULTS

The girl carried a maternal balanced translocation 46,X,t(X;1)(q28;p31.1). Whole-exome sequencing revealed no monogenic mutation related to her phenotype, but she carried a rare skewed inactivation of the translocated X chromosome that spread to the adjacent interstitial 1p segment, contrary to her mother. All translocation breakpoints in cases 1-3 were successfully identified and each couple underwent one PGT cycle. Thirty oocytes were retrieved, and 13 blastocysts were eligible for biopsy, of which six embryos had a balanced translocation and only four were non-carriers. Three cryopreserved embryo transfers with non-carrier status embryos resulted in the birth of two healthy children (one girl and one boy), who were subsequently confirmed to have normal karyotypes.

CONCLUSIONS

This study reported a girl with multiple congenital disabilities associated with a maternal balanced t(X-A) and verified that the distinction between non-carrier and carrier embryos is an effective and applicable strategy to avoid transferring genetic and reproductive risks to the offspring of t(X-A) carriers.

The decision on the embryo to transfer after Preimplantation Genetic Diagnosis for X-autosome reciprocal translocation in male carrier

Background

The aim of Preimplantation Genetic Diagnosis (PGD) on embryos produced in vitro is to identify the embryos without genetic or chromosomal defect from those embryos that will develop the genetic disease or are chromosomally abnormal. In case of PGD for structural chromosome indication (PGR-SR), the normal/balanced embryos are transferred in the maternal uterus. This protocol is valid and widely applied for autosomal chromosome translocation. But which embryo should be transferred after preimplantation genetic diagnosis (PGD-SR) for X-3 reciprocal translocation in male patient?

Case presentation

The female patient was 26 years old with normal 46,XX karyotype. The male patient had a karyotype with balanced translocation 46,Y,t(X;3)(p11.2;p14)mat, inherited from the mother. The female patient underwent two cycles of ovarian stimulation. In the first cycle, the metaphase II oocytes were vitrified, while in the second cycle they were used as fresh. ICSI was performed on vitrified/warmed and fresh oocytes. Embryos were biopsied at blastocyst stage. Chromosomal analysis was performed by Next Generation Sequencing.

Eleven blastocysts were biopsied from 23 vitrified/warmed and fresh metaphase II oocytes. Two embryos were diagnosed 46,XY; two embryos were diagnosed 46,XX; four embryos were diagnosed with unbalanced translocations and three embryos were diagnosed aneuploid. We knew that the two embryos diagnosed as 46,XX inherited the balanced translocation from the father and the two embryos diagnosed as 46,XY had a normal karyotype. It was explain to the couple that the phenotype of balanced translocated female embryos cannot be predicted because of the random inactivation of X chromosome and that could also occur on the der(X). The couple asked to have a 46,XY embryo transferred. Clinical pregnancy was obtained and non invasive prenatal test confirmed PGD-SR result.

Conclusions

Proposing PGD-SR for gonosome-autosome reciprocal translocation implies the risk to exclude balanced translocated female embryos with a normal phenotype for transfer because the early and late normal development at post-natal stage cannot be predicted based on the only chromosomal analysis.

Perinatal follow-up of children born after preimplantation genetic diagnosis between 1995 and 2014

Purpose

We aim to evaluate the safety of PGD. We focus on the congenital malformation rate and additionally report on adverse perinatal outcome.

Methods

We collated data from a large group of singletons and multiples born after PGD between 1995 and 2014. Data on congenital malformation rates in live born children and terminated pregnancies, misdiagnosis rate, birth parameters, perinatal mortality, and hospital admissions were prospectively collected by questionnaires.

Results

Four hundred thirty-nine pregnancies in 381 women resulted in 364 live born children. Nine children (2.5%) had major malformations. This percentage is consistent with other PGD cohorts and comparable to the prevalence reported by the European Surveillance of Congenital Anomalies (EUROCAT). We reported one misdiagnosis resulting in a spontaneous abortion of a fetus with an unbalanced chromosome pattern. 20% of the children were born premature (< 37 weeks) and less than 15% had a low birth weight. The incidence of hospital admissions is in line with prematurity and low birth weight rate. One child from a twin, one child from a triplet, and one singleton died at 23, 32, and 37 weeks of gestation respectively.

Conclusions

We found no evidence that PGD treatment increases the risk on congenital malformations or adverse perinatal outcome.

Trial registration number

NCT 2 149485

Electronic supplementary material

The online version of this article (10.1007/s10815-018-1286-2) contains supplementary material, which is available to authorized users.

Präimplantationsdiagnostik in den Niederlanden

Im Jahr 1995 wurde die Präimplantationsdiagnostik (PID) auf experimenteller Ebene in Maastricht eingeführt. Seit 2003 ist sie Bestandteil des Erstattungssystems des niederländischen Ministry Public Health, Welfare and Sport.

PID wird nur Paaren ermöglicht, die mit einem Risiko für eine schwerwiegende monogene Erkrankung, strukturellen Chromosomenanomalien oder mitochondrialen Erkrankungen bei ihren Nachkommen rechnen müssen. Ein Aneuploidiescreening zur Verbesserung der Erfolgsraten und assistierte Reproduktionstechnologien wie In-vitro-Fertilisation (IVF) oder Intrazytoplasmatische Spermieninjektion (ICSI) waren nie Gegenstand des PID-Programms.

2008 beschloss die niederländische Regierung, eine „National Indications Commission“ einzurichten, die bei neuen Krankheitsentitäten prüfen soll, ob die Kriterien für die Zulassung einer PID erfüllt sind: 1. die Schwere und Art der Erkrankung, 2. bestehende Möglichkeiten für Prävention und Behandlung, 3. zusätzliche medizinische Kriterien und 4. psychologische und ethische Faktoren.

Geschlechtsbestimmung (aus sozialen Gründen) ist auch in den Niederlanden, wie in den meisten europäischen Ländern, nicht erlaubt. Eine PID für die Diagnose sog. Rettungskinder ist nur dann erlaubt, wenn unabhängig hiervon eine Indikation für eine PID der genetischen Erkrankung besteht. HLA-Typisierung ohne Indikation für eine genetische Erkrankung ist hingegen nicht zulässig.

Das Maastricht University Medical Center (UMC) übernimmt die gesamte genetische Diagnostik und verfügt über die mit den Universitäten von Utrecht, Groningen und Amsterdam abgestimmten (University Medical Centre (UMC) Utrecht, University Medical Centre (UMC) Groningen and the Amsterdam Medical Centre (AMC)) SOPs für die PID-Transporte.

Zwischen 1995 und 2015 wurden insgesamt 2870 Zyklen bei 1430 Paaren durchgeführt. Der häufigste Grund für eine Überweisung zur PID war die Huntington-Krankheit, gefolgt von erblichem Brust- und Eierstockkrebs. Unter den weiteren Indikationen sind weit mehr autosomal-dominante genetisch bedingte Erkrankungen als autosomal-rezessive. Unter den zuletzt genannten stehen an erster Stelle Mukoviszidose und danach die spinale Muskelatrophie (SMA). Die Erfolgsrate liegt bei 20 % pro Zyklusbeginn und bei 25 % pro Embryonentransfer. Die Anzahl der Behandlungszyklen pro Paar liegt fast exakt bei 2,0.

Translocations, inversions and other chromosome rearrangements

Chromosomal rearrangements have long been known to significantly impact fertility and miscarriage risk. Advancements in molecular diagnostics are challenging contemporary clinicians and patients in accurately characterizing the reproductive risk of a given abnormality. Initial attempts at preimplantation genetic diagnosis were limited by the inability to simultaneously evaluate aneuploidy and missed up to 70% of aneuploidy in chromosomes unrelated to the rearrangement. Contemporary platforms are more accurate and less susceptible to technical errors. These techniques also offer the ability to improve outcomes through diagnosis of uniparental disomy and may soon be able to consistently distinguish between normal and balanced translocation karyotypes. Although an accurate projection of the anticipated number of unbalanced embryos is not possible at present, confirmation of normal/balanced status results in high pregnancy rates (PRs) and diagnostic accuracy.

Is the resulting phenotype of an embryo with balanced X-autosome translocation, obtained by means of preimplantation genetic diagnosis, linked to the X inactivation pattern?

OBJECTIVE

To examine if a balanced female embryo with X-autosome translocation could, during its subsequent development, express an abnormal phenotype.

DESIGN

Preimplantation genetic diagnosis (PGD) analysis on two female carriers with maternal inherited X-autosome translocations.

SETTING

Infertility center and genetic laboratory in a public hospital.

PATIENT(S)

Two female patients carriers undergoing PGD for a balanced X-autosome translocations: patient 1 with 46,X,t(X;2)(q27;p15) and patient 2 with 46,X,t(X;22)(q28;q12.3).

INTERVENTION(S)

PGD for balanced X-autosome translocations.

MAIN OUTCOME MEASURE(S)

PGD outcomes, fluorescence in situ hybridization in biopsied embryos and meiotic segregation patterns analysis of embryos providing from X-autosome translocation carriers.

RESULT(S)

Controlled ovarian stimulation facilitated retrieval of a correct number of oocytes. One balanced embryo per patient was transferred and one developed, but the patient miscarried after 6 weeks of amenorrhea. In X-autosome translocation carriers, balanced Y-bearing embryos are most often phenotypically normal and viable. An ambiguous phenotype exists in balanced X-bearing embryos owing to the X inactivation mechanism. In 46,XX embryos issued from an alternate segregation, der(X) may be inactivated and partially spread transcriptional silencing into a translocated autosomal segment. Thus, the structural unbalanced genotype could be turned into a viable functional balanced one. It is relevant that a discontinuous silencing is observed with a partial and unpredictable inactivation of autosomal regions. Consequently, the resulting phenotype remains a mystery and is considered to be at risk of being an abnormal phenotype in the field of PGD.

CONCLUSION(S)

It is necessary to be cautious regarding to PGD management for this type of translocation, particularly in transferred female embryos.

Understanding the Complex Circuitry of lncRNAs at the X-inactivation Center and Its Implications in Disease Conditions

Balanced gene expression is a high priority in order to maintain optimal functioning since alterations and variations could result in acute consequences. X chromosome inactivation (X-inactivation) is one such strategy utilized by mammalian species to silence the extra X chromosome in females to uphold a similar level of expression between the two sexes. A functionally versatile class of molecules called long noncoding RNA (lncRNA) has emerged as key regulators of gene expression and plays important roles during development. An lncRNA that is indispensable for X-inactivation is X-inactive specific transcript (Xist), which induces a repressive epigenetic landscape and creates the inactive X chromosome (Xi). With recent advents in the field of X-inactivation, novel positive and negative lncRNA regulators of Xist such as Jpx and Tsix, respectively, have broadened the regulatory network of X-inactivation. Xist expression failure or dysregulation has been implicated in producing developmental anomalies and disease states. Subsequently, reactivation of the Xi at a later stage of development has also been associated with certain tumors. With the recent influx of information about lncRNA biology and advancements in methods to probe lncRNA, we can now attempt to understand this complex network of Xist regulation in development and disease. It has become clear that the presence of an extra set of genes could be fatal for the organism. Only by understanding the precise ways in which lncRNAs function can treatments be developed to bring aberrations under control. This chapter summarizes our current understanding and knowledge with regard to how lncRNAs are orchestrated at the X-inactivation center (Xic), with a special focus on how genetic diseases come about as a consequence of lncRNA dysregulation.

Is the interchromosomal effect present in embryos derived from Robertsonian and reciprocal translocation carriers particularly focusing on chromosome 10 rearrangements?

The aim of this study was to analyse the possible occurrence of the interchromosomal effect (ICE) in human preimplantation embryos obtained from Robertsonian and reciprocal translocation carriers focusing on ones with chromosome 10 rearrangements who were undergoing preimplantation genetic diagnosis (PGD) and to investigate whether offering aneuploidy screening would be beneficial to these patients. Cleavage stage embryos from translocation carriers undergoing PGD were biopsied. Multicolour fluorescence in situ hybridisation for the chromosomes involved in the translocation in addition to nine more chromosomes (13, 15, 16, 17, 18, 21, 22, X and Y) was used in the analysis. The control group involved embryos obtained from age-matched patients undergoing preimplantation genetic screening (PGS). Cumulative aneuploidy rate in embryos derived from both Robertsonian and reciprocal translocation carriers was found to be similar with the control group. Therefore no ICE was observed in cleavage stage embryos obtained from these carriers. More than half of the embryos with chromosome 10 rearrangements had aneuploidy for which an increased aneuploidy rate was more apparent in male carriers. Thus, it is possible that there is a risk of ICE in reciprocal carriers with chromosome 10 rearrangements. This study showed that there is no ICE in embryos derived from Robertsonian and reciprocal translocation carriers. However high rates of aneuploidy in structurally normal chromosomes were detected in embryos derived from these carriers and thus aneuploidy screening in addition to PGD may increase the pregnancy rates of these patients.

Poor embryo development and preimplantation genetic diagnosis outcomes of translocations involving chromosome 10: Do we blame genetics?

Balanced reciprocal translocation carriers are usually phenotypically normal. Although the reproductive risk of these carriers varies, they generally have a lower chance to produce normal or balanced gametes. Preimplantation genetic diagnosis (PGD) is offered to these patients to increase their chances of becoming pregnant by selecting a balanced embryo for transfer. This study aimed to analyse the development and the PGD outcome of the embryos obtained from reciprocal translocation carriers focusing on ones with chromosome 10 rearrangements. In total, 27 reciprocal translocation carriers underwent 31 cycles of PGD. PGD was performed using multicolour fluorescence in situ hybridisation for 298 embryos and of these 136 were obtained from couples carrying translocations involving chromosome 10 rearrangements. Carriers of translocations involving chromosome 10 rearrangements have a lower chance of producing normal or balanced embryos compared with the carriers with other rearrangements. The development of embryos obtained from the patients with chromosome 10 rearrangements was impaired and only a limited number of embryos developed to the blastocyst stage.