The establishment and application of preimplantation genetic haplotyping in embryo diagnosis for reciprocal and Robertsonian translocation carriers

Shuo Zhang,Jing Zhou,Caixia Lei,Junping Wu,Xiaoxi Sun,Yijuan Sun,Daru Lu,Haiyan Sun,Jing Fu,Yueping Zhang

doi:10.1186/s12920-017-0294-x

Abstract

BackgroundPreimplantation genetic diagnosis (PGD) is now widely used to select embryos free of chromosomal copy number variations (CNV) from chromosome balanced translocation carriers. However, it remains a difficulty to distinguish in embryos between balanced and structurally normal chromosomes efficiently.MethodsFor this purpose, genome wide preimplantation genetic haplotyping (PGH) analysis was utilized based on single nucleotide polymorphism (SNP) microarray. SNPs that are heterozygous in the carrier and, homozygous in the carrier’s partner and carrier’s family member are defined as informative SNPs. The haplotypes including the breakpoint regions, the whole chromosomes involved in the translocation and the corresponding homologous chromosomes are established with these informative SNPs in the couple, reference and embryos. In order to perform this analysis, a reference either a translocation carrier’s family member or one unbalanced embryo is required. The positions of translocation breakpoints are identified by molecular karyotypes of unbalanced embryos. The recombination of breakpoint regions in embryos could be identified.ResultsEleven translocation families were enrolled. 68 blastocysts were analyzed, in which 42 were unbalanced or aneuploid and the other 26 were balanced or normal chromosomes. Thirteen embryos were transferred back to patients. Prenatal cytogenetic analysis of amniotic fluid cells was performed. The results predicted by PGH and karyotypes were totally consistent.ConclusionsWith the successful clinical application, we demonstrate that PGH was a simple, efficient, and popularized method to distinguish between balanced and structurally normal chromosome embryos.

Highlights

Preimplantation genetic diagnosis (PGD) is widely used to select embryos free of chromosomal copy number variations (CNV) from chromosome balanced translocation carriers
Microarray technologies and next-generation sequencing (NGS) which are capable of testing for chromosome translocation imbalances and screening for aneuploidy of all 23-pairs of chromosomes simultaneously have been widely used in many centers [9,10,11,12]
Despite having a successful PGD cycle and delivery in translocation families, many of these couples will be passing on the translocation to their children who may be subjected to infertility, recurrent pregnancy loss or even have to seek assisted reproductive technologies to conceive

Summary

Introduction

Preimplantation genetic diagnosis (PGD) is widely used to select embryos free of chromosomal copy number variations (CNV) from chromosome balanced translocation carriers. Studies performed previously indicate that array-based PGD can improve pregnancy rates in translocation carrier couples to between 45%-70% per transfer [12,13,14] Despite this advantage, these traditional PGD methods can’t distinguish balanced and structurally normal embryos from translocation carriers. In the latest research of Hu et al [18], the authors developed a “MicroSeq-PGD” method which combined chromosome microdissection and NGS in reciprocal translocation carriers to characterize the DNA sequence of the translocation breakpoints to distinguish embryos. These methods are possibly time-consuming, complicated, and homologous recombination can’t be identified. Robertsonian translocation carriers are not included, which have an estimated 0.1% incidence rate in the general population [19]

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