Preimplantation genetic diagnosis for couples with a Robertsonian translocation: practical information for genetic counseling

Purpose  

To evaluate the proportions of abnormal and normal embryos detected by preimplantation genetic diagnosis (PGD) of infertile couples of whom one was a Robertsonian translocation (RT) carrier, and to provide practical information, including details of reproductive outcomes, to aid in genetic counseling of such couples.     

Outcome of preimplantation genetic diagnosis of translocations

Objective: To review 35 cases of preimplantation genetic diagnosis (PGD) of translocations with several methods, including telomeric probes.

Design: Retrospective study.

Setting: Clinical IVF laboratory.

Patient(s): Thirty-five couples with one partner carrying a chromosomal translocation.

Intervention(s): PGD of translocation after polar-body or embryo biopsy.

Main Outcome Measure(s): Pregnancy outcome.

Result(s): Several trends were observed. First, PGD can achieve a statistically significant reduction in spontaneous abortion, from 95% to 13%. Second, the chances of achieving pregnancy are correlated with 50% or more of the embryos being chromosomally normal. Third, patients with robertsonian translocations produced fewer abnormal gametes and more pregnancies than did patients with reciprocal translocations. Fourth, a new fluorescence in situ hybridization protocol for PGD of translocations, which involves applying telomeric probes, has proved adequately reliable with a 6% average error rate.

Conclusion(s): PGD of translocations achieves a statistically significant reduction in spontaneous abortion, both for polar-body and blastomere biopsy cases. Pregnancy outcome depended on the number of normal embryos available for transfer, with patients having <50% abnormal embryos achieving the most pregnancies. Because robertsonian translocations caused fewer abnormal embryos than reciprocal translocations, they also resulted in higher rates of implantation.     

Preimplantation genetic diagnosis

Since its introduction in 1990, preimplantation genetic diagnosis (PGD) has allowed embryo genetic analysis prior to transfer into the uterus during an in vitro fertilisation (IVF) cycle. The commonest indications are for detection of single-gene, X-linked, structural chromosomal and mitochondrial disorders as well as for Human Leucocyte Antigen matching. Traditional cytogenetic and molecular techniques of fluorescent in situ hybridization and polymerase chain reaction are complemented by newer technologies e.g. array comparative genomic hybridization and whole genome amplification. Following a successful PGD cycle, pregnancy complications are comparable to those in standard IVF/intra-cytoplasmic sperm injection (ICSI) cycles, which are mostly related to preterm delivery due to multiple pregnancies. There are similar rates of congenital malformations, neonatal morbidity and developmental outcomes in children born after PGD compared with those born after IVF/ICSI. Clinical outcome data is collected by the Preimplantation Genetics International Society and the European Society for Human Reproduction and Embryology PGD Consortium.     

短串联重复序列在染色体罗氏易位植入前遗传学诊断的应用

目的:采用多重置换扩增(MDA)结合短串联重复序列(STR)建立一种基于PCR技术诊断染色体罗氏易位的植入前遗传学诊断(PGD)方法。方法:选择位于易位染色体上的STR位点,对家系采用荧光PCR进行分析,选择有多态性的位点,再采用MDA对单细胞进行全基因组扩增,根据家系分析的结果,对具有多态性的STR位点进行分析诊断。结果:对3个家系进行了4个取卵周期(3个PGD周期),每个家系分别采用7~15个具有多态性的STR位点进行分析,共对24个胚胎进行诊断。PGD的诊断效率为95.8%(23/24),平衡胚胎占52.2%(12/23),异常胚胎占47.8%(11/23),共移植了6个胚胎,获得2例临床妊娠,临床妊娠率为66.7%(2/3),出生了2个健康婴儿,染色体核型均正常。结论:采用依赖于STR的PCR分析法可以用于染色体罗氏易位的PGD。     

Preimplantation genetic diagnosis

This article aims to inform about the current practices in Preimplantation Genetic Diagnosis (PGD) from a United Kingdom perspective. Progress in the field has been marked over the last decade and new techniques have superseded traditional analysis. The review moves from governance and data collection for PGD to the patient journey. We discuss embryo biopsy and the challenges of analysis when starting with a small amount of DNA. Segments are introduced which introduce basic principles to allow better appreciation of the tests and when they should be applied. We discuss PGD for single gene disorders by preimplantation genetic haplotyping, including for autosomal dominant de novo mutations. Translocations are also discussed and PGD by microarray analysis. We conclude by considering next generation sequencing with the advantages and challenges this may provide to the field.     

Poor prognosis of recurrent aborters with either maternal or paternal reciprocal translocations

OBJECTIVE: To determine whether the miscarriage rate in recurrent miscarriage patients with an abnormal karyotype, especially reciprocal translocations, in either partner is worse than without an abnormal karyotype. DESIGN: Retrospectively analyzed prospectively obtained database. SETTING: Nagoya City University Hospital. PATIENT(S): One thousand and two hundred eighty-four couples with a history of 2 or more (2 to 12) consecutive first-trimester miscarriages. INTERVENTION(S): Patients with antiphospholipid antibodies were treated with low-dose aspirin and combined therapy. MAIN OUTCOME MEASURE(S): Subsequent miscarriages were compared for cases with and without an abnormal karyotype in either partner. A karyotype analysis was also conducted for each aborted conceptus and offspring of 95 pregnancies of 47 patients with reciprocal translocations. RESULT(S): Of the total of 1,284 couples, 58 (4.5%) had translocations, 11 being Robertsonian translocations. Eleven of the 18 cases (61.1%) where the husband had a reciprocal translocation suffered further miscarriage; this also was the case for 21 of the 29 cases (72.4%) where the wives had a reciprocal translocation. Those with reciprocal translocations in either partner miscarried significantly more frequently than those without an abnormal karyotype. Only one infant with an unbalanced translocation was found in 34 cases of successful pregnancy following habitual abortion. CONCLUSION(S): The pregnancy prognosis with either maternal or paternal reciprocal translocations is poorer than without them. The presence of a reciprocal translocation is thus a risk factor in couples who have recurrent miscarriages.     

应用荧光原位杂交技术进行植入前胚胎染色体诊断的价值

目的 初步探讨应用荧光原位杂交(FISH)技术进行植入前胚胎染色体诊断的价值。方法 对10对不孕夫妇进行植入前遗传学诊断(PGD)周期的超促排卵和卵母细胞浆内单精子注射,于受精后第3天进行胚胎活检及FISH分析,第4天选择染色体组成正常或平衡的胚胎进行移植。结果 10个PGD周期共获卵158个,对其中54个胚胎进行活检,51个胚胎获得明确诊断,诊断率为94％(51／54)。对染色体组成正常或平衡的24个胚胎进行官腔内移植,共4例获得妊娠,其中3例已足月分娩健康婴儿,1例为异位妊娠。结论 应用FISH技术进行植人前胚胎染色体诊断,是预防流产和染色体异常患儿出生的有效手段。     

Preimplantation genetic diagnosis by fluorescence in situ hybridization: clinical possibilities and pitfalls

Preimplantation genetic diagnosis using the fluorescence in situ hybridization technique (FISH) is being used widely to prevent the transmission of sex-linked diseases, to screen for translocations, and for aneuploidy screening in specific in vitro fertilization (IVF) patient groups, along with FISH analysis of spermatozoa in infertile men. In this study, we aim to critically analyze our clinical results in patients at risk of transmitting sex-linked diseases (n = 55), in carriers of translocations (n = 43), in women who have recurrent miscarriage (two or more miscarriages) (n = 128), recurrent IVF failure (three or more failed IVF attempts) (n = 47), and patients of advanced maternal age (37 years old or older) (n = 79). The use of the FISH technique in carriers of sex-linked diseases and translocation patients prevents transmission of these conditions and provides good IVF outcome. In patients with recurrent miscarriage, implantation failure, and advanced maternal age, a high incidence of embryos with abnormal chromosomes 13,16,18,21,22, X, and Y was observed (range 69-75%), as expected. In those three groups of patients, the selection of euploid embryos for transfer resulted in good pregnancy rates with a low incidence of miscarriage. Limitations and pitfalls of this technique are also discussed.     

Preimplantation genetic diagnosis

Pre-Implantation genetic diagnosis is available to couples at risk of conceiving a pregnancy affected with a known genetic disorder. Assisted reproductive techniques are used in combination with micromolecular diagnostic technologies to recognise at-risk embryos with pathogenic genetic variants at the pre-implantation stage using polar body, blastomere or trophectoderm biopsy. This review will discuss the varying genetic disorders diagnosed by Pre-Implantation Genetic Diagnosis, as well as the ethical, legal and safety implications of the process. Pioneering advances in molecular biology and cytogenomics have been utilised to expand the spectrum of genetic disorders detected.     

Higher degree of chromosome mosaicism in preimplantation embryos from carriers of robertsonian translocation t(13;14) in comparison with embryos from karyotypically normal IVF patients

Purpose : To compare the frequency and the degree of mosaicism in human embryos from Robertsonian translocation (RT) t(13;14) carriers, with embryos from karyotypically normal IVF patients. Methods : FISH analysis of embryos from PGD cycles for RT t(13;14), with probes for chromosomes 13, 14, and 18 (Group I) and of embryos from karyotypically normal IVF patients with probes for chromosomes 13, 18, 21, X, and Y (Group II). Results : The incidence of abnormal mosaic embryos was significantly higher in group I (38/51) as compared with group II (6/45) (²: P < 0.01). Furthermore, in group I the percentage of diploid cells per embryo was lower for chromosome 13 and 14 in comparison with 18, while in group II no differences were observed between the five chromosomes analyzed. Conclusions : RT induces a high frequency of mosaicism specifically for the chromosomes implicated in the translocation; the analysis by FISH of two blastomeres is strongly recommended for these patients.     

植入前遗传学诊断及筛查咨询

随着分子生物学技术的飞速发展及其在生殖领域的应用,植入前遗传学诊断（PGD）、植入前遗传学筛查（PGS）的遗传咨询变得更加复杂。在PGD、PGS的遗传咨询中,医生应充分告知患者PGD、PGS的应用现状、利弊、可能的预后、技术缺陷与安全性问题。同时,经PGD、PGS成功妊娠的孕妇,仍需进行常规的产前诊断,这一点对于PGD、PGS的安全性至关重要。