Incidence of Chromosomal Mosaicism in Human Embryos at Different Developmental Stages Analyzed by Fluorescence In Situ Hybridization

Abstract

Chromosomal mosaicism has been reported in in vitro-cultured embryos at early cleavage stages, as well as in morulae and blastocysts. We have assessed the incidence and pattern of mosaicism during in vitro development of human embryos from early-cleavage stages to morula and blastocyst. Fifty spare embryos were fixed for fluorescence in situ hybridization (FISH) analysis for chromosomes X, Y, 13, 18, and 21 on days 2 or 3 (4- to 10-cell stage) (n = 16), on day 4 (morula stage) (n = 14), on day 5 (pre-expanded blastocyst) (n = 5), and the expanded blastocyst stages (n = 15). Blocked embryos (no cleavage observed within the last 24 hr) were not included. A total of 2367 cells were analyzed. Four early-cleavage stage embryos were found uniformly diploid; all of the others were mosaic for the chromosomes analyzed (mean diploid nuclei 48.3% +/- 28.7). All of the embryos at more advanced developmental stages, except one fully normal morula, had mosaic chromosome constitutions, with an increase in the percentage of diploid cells in morulae, pre-expanded, and expanded blastocysts, respectively (mean diploid nuclei 78.6% +/- 11.7, 66.0% +/- 20.8, 79.6% +/- 12.8), in comparison with earlier stages. Hypotheses about the origin of mosaicism and embryo regulation mechanisms will be discussed.

PGS-FISH in reproductive medicine and perspective directions for improvement: a systematic review

“…Among the causes of these controversies are the above-mentioned technical ones, in addition to those of a physiological nature. It is well documented that chromosomal mosaicism occurs in early human stage embryos [26,[48][49][50][51]. At least 40-50% of human embryos are chromosomally mosaic, while some present such high levels of abnormalities that they are considered to be completely chaotic [52].…”

A prospective randomized controlled trial of preimplantation genetic screening in the “good prognosis” patient

“…There is much debate about the role and frequency of mosaicism in the early embryo (42)(43)(44)(45). Certainly, a single biopsied cell may not represent the true chromosomal makeup of the embryo, and, as such, some proportion of the abnormally diagnosed embryos may well have contained normal cells.…”

Aneuploidy study in sperm and preimplantation embryos from nonmosaic 47,XYY men

“…All probes were directly labeled and purchased from Vysis Inc. The two-round FISH procedure was performed as described elsewhere, but for five-chromosome detection (16). Probes for chromosomes X (CEP X, 1:1 spectrum green þ spectrum orange mixture), Y (CEP Y, spectrum orange), 18 (CEP 18, spectrum aqua), and 22 (LSI 22, spectrum green) were applied in the first round, and those for chromosomes 13 (LSI 13, spectrum green), 16 (CEP 16, spectrum aqua), and 21 (LSI 21, spectrum orange), in the second round.…”