Identification of biparental and diploid blastocysts from monopronuclear zygotes with the use of a single-nucleotide polymorphism array

Abstract

Objective: To select normal fertilized diploid blastocysts in patients who had only monopronucleated (1PN) embryos for transfer.

Design: Experimental study.

Setting: University-affiliated center.

Patient(s): Couples who were undergoing intracytoplasmic sperm injection treatment and had 1PN blastocysts.

Intervention(s): In a preliminary test, limited cells of parthenogenetic human embryonic stem cells (phESCs) and normal fertilized blastocysts were analyzed with the use of a low-density single-nucleotide polymorphism (SNP) array to identify the distribution pattern and rate of heterozygosity. In the clinical application, 1PN blastocysts were analyzed with the use of the SNP array. Only diagnosed normal blastocysts were transferred. The diagnosed uniparental blastocysts were validated by imprinted gene expression.

Main outcome measure(s): Distribution pattern and rate of heterozygosity between parthenogenesis and normal fertilization.

Result(s): In the pretest, phESCs exhibited distinct distribution pattern and lower rate of heterozygosity, compared with normal fertilized blastocysts after SNP analysis. In particular, homozygous hESCs showed a panhomozygosity distribution pattern, hybrid phESCs showed a partial homozygosity distribution pattern, and normal fertilized blastocysts exhibited a panheterozygosity distribution pattern with an average of 20.21% heterozygosity rate; 13.6% was found to be the minimum cutoff to predict normal fertilized samples. In the clinical application, 24 1PN blastocysts were analyzed; 10/24 showed chromosomal abnormalities, 3/24 showed panhomozygosity with 0.45%-0.8% heterozygosity, and 1/24 showed partial homozygosity with 6.54% heterozygosity. The remaining 10 blastocysts, with a panheterozygosity distribution pattern and higher genomic heterozygosity rate, were diagnosed as normal-fertilization diploid embryos; three were transferred and resulted in two healthy newborns.

Conclusion(s): The low-density SNP array might serve as a cost-effective method to identify biparental origin and diploid 1PN blastocysts for transfer.

Keywords: Loss of heterozygosity; monopronuclear zygote; preimplantation genetic screening; single-nucleotide polymorphism; uniparental.