MOSAICISM OF AUTOSOMES AND SEX-CHROMOSOMES IN MORPHOLOGICALLY NORMAL,MONOSPERMIC PREIMPLANTATION HUMAN EMBRYOS

We have previously detected chromosome abnormalities in human embryos whilst identifying the sex for preimplantation diagnosis of X-linked d isease. In this study we assess the incidence of these abnormalities, both for sex chromosomes and autosomes I and 17, using dual fluorescen t in situ hybridization (FISH). Sixty-nine normally fertilized embryos of good morphology at the 6-10 cell stage (day 3 post-insemination) w ere examined. The embryos were spread whole using HCl and Tween 20 to dissolve the cytoplasm. Thirty-four embryos were analysed for the sex chromosomes and 35 for autosomes 1 and 17. All probes were directly la belled with fluorochromes allowing analysis in 2h. Control lymphocytes demonstrated that the probes were of high specificity. For the sex ch romosomes, five embryos were mosaic (15 per cent) with the remaining 2 9 being uniformly XX or XY. In no case was an XX nucleus found in an o therwise XY embryo, indicating that even though mosaicism for the sex chromosomes is present, such abnormalities would not lead to a misdiag nosis of sex. For the autosomes, 16 embryos were abnormal (46 per cent ); one embryo was triploid, one was monosomic for chromosome 1, and te n others were diploid mosaics (three diploid/aneuploid, three diploid/ polyploid, and four diploid/haploid). A further four embryos had varia ble chromosome numbers in the majority of nuclei which appeared to be the result of uncontrolled mitotic division. The presence of haploidy or double monosomy, which occurred in 15 per cent of nuclei, has impor tant implications for the diagnosis of trisomies and dominant disorder s.