Determination of the genetic status of cleavage-stage human embryos by microsatellite marker analysis following multiple displacement amplification

Objectives: To analyse genotype information from cleavage-stage human embryos and assess the chromosomal status and feasibility of performing aneuploidy screening by microsatellite analysis. Methods: DNA from 49 blastomeres from eight cleavage-stage human embryos was amplified using multiple displacement amplification, then tested for panels of 64 polymorphic microsatellite markers on seven different chromosomes, and for two non-polymorphic sequences on the X and Y chromosomes. Results: There was an overall allele drop out (ADO) rate of 28%. Novel alleles in single cells were seen in 0.3% of amplifications, interpreted as either somatic microsatellite mutation events or 'slippage' of the MDA φ 29 polymerase. Three-allele results for a single marker in a single cell were found in 0.07% of amplifications, interpreted as 'slippage' of the MDA φ 29 polymerase. One apparent segmental duplication was found. Only one embryo with no normal cells was found, probably arising from the chaotic cleavage division following a triploid conception. Six embryos were mosaic, of which four had only one abnormal cell. Conclusions: Abnormalities in human embryos may be present in only a single cell, leading to potentially false abnormal results at pre-implantation genetic diagnosis. ADO associated with MDA reduces the efficacy of this approach for detection of aneuploidy. Statistical analysis showed that, for ADO of 28%, seven informative markers would be required to give 95% confidence of detecting trisomic embryos.