Background: Spatial organization of chromosomes is hypothesized to reflect transcriptional activity and regulatory protein function. Preimplantation genetic diagnosis allows assessment of the spatial relationship of chromosomes in human blastomeres. We thus examined the localization of chromosomes 13, 16, 18, 21, 22, X and Y in blastomeres from 6-8-cell stage embryos, correlating localization to aneuploidy and embryo morphology.
Methods: Following fluorescence in situ hybridization to enumerate chromosomes 13, 16, 18, 21, 22, X and Y, signal positions were localized within one of four concentric shells. Statistical analysis compared chromosome localization between euploid and aneuploid blastomeres as well as morphologically normal and abnormal embryos.
Results: Of 98 embryos, 109 blastomeres were evaluated. Within chromosomally normal blastomeres, no difference in the location of all seven chromosomes (P</=0.10) was observed. However, a significant difference was observed between the organization of chromosomes in euploid versus aneuploid blastomeres (P</=0.001). Localization of chromosomes 13, 18, 21 and 22 was significantly different when an abnormality involving that chromosome existed (P</=0.001, P</=0.01, P</=0.025 and P</=0.01 respectively).
Conclusions: We report for the first time that localization of chromosomes is altered in chromosomally aneuploid but not in chromosomally normal nor morphologically abnormal euploid blastomeres.