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

Abstract

Background: Preimplantation 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.

Methods: For 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.

Results: Eleven 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.

Conclusions: With the successful clinical application, we demonstrate that PGH was a simple, efficient, and popularized method to distinguish between balanced and structurally normal chromosome embryos.

Keywords: Breakpoint; Preimplantation genetic haplotyping; Reciprocal translocation; Robertsonian translocation; Single nucleotide polymorphism.

Fig. 1

The process of establishing haplotypes and distinguishing between balanced and structurally normal chromosomes embryos through PGH analysis. Informative SNPs should be heterozygous in the carrier, and homozygous in the carrier’s partner and carrier’s family member. These SNPs were used to establish the haplotypes of the breakpoint regions, the whole chromosomes involved in the translocation and the corresponding normal homologous chromosomes in the couple, reference and embryos

Fig. 2

a The genealogic tree in family3. b The peripheral blood karyotype of carrier, the translocation was inherited from her father. c Based on the genetic screening of 23-pairs chromosomes, embryo-1 and embryo-6 were identified as balanced or normal embryos, embryo-2 was identified as unbalanced embryo. d The haplotypes including the two breakpoint regions, the two whole chromosomes involved in the translocation and the two corresponding normal homologous chromosomes in the couple, reference who has the same translocation and embryos were shown. The recombination was identified outside the breakpoints. The colorful histograms represented haplotypes, in the embryos the gray column represented the haplotype that was inherited from the normal parent and in the carrier’s family number the gray column represented the haplotype that wasn’t passed on to the carrier, the other different colorful histograms represented different haplotypes. The PGH result indicated embryo-6 was a translocation carrier embryo and embryo-1 was a structurally normal embryo