Incidence of chromosomal mosaicism in morphologically normal nonhuman primate preimplantation embryos

Objective: To establish the exact rates of chromosomal mosaicism in morphologically normal rhesus macaque embryos by determining the chromosomal complement of all blastomeres. Design: Retrospective rhesus monkey IVF study. Setting: Academic laboratory and primate research center. Patient(s): Young fertile rhesus macaque females. Intervention(s): Morphologically normal in vitro-produced rhesus macaque embryos were dissociated and cytogenetically assessed using a five-color fluorescent in situ hybridization assay developed for rhesus macaque chromosomes homologous to human chromosomes 13, 16, 18, X, and Y. Main Outcome Measure(s): The incidence and extent of chromosomal mosaicism in rhesus macaque preimplantation embryos. Result(s): Seventy-seven preimplantation embryos, displaying normal morphology and development, from 17 young rhesus macaque females were analyzed. Overall, 39 embryos (50.6%) were normal, 14 embryos (18.2%) were completely abnormal, and 24 embryos (31.2%) were mosaic. Of the 226 blastomeres analyzed in the mosaic group, 110 blastomeres (48.7%) were normal. Conclusion(s): The observed rate of mosaicism in good-quality rhesus embryos resembles previously documented frequencies in poor-quality human preimplantation embryos. A high incidence of mosaicism may limit the diagnostic accuracy of preimplantation genetic diagnosis.