A canadian collaborative study of mosaicism in amniotic fluid cell cultures

Abstract

Data on chromosomal mosaicism was collected retrospectively on 12 386 amniotic fluid samples cultured over a 10 year period in 14 Canadian centres. Level I mosaicism (a single abnormal cell--excluding single cell monosomy) was encountered in 863 cases (7.1 per cent). Level II mosaicism (multiple cells with the same abnormality in a single flask or colony) was encountered in 138 cases (1.1 per cent). Level III mosaicism (multiple cells distributed over multiple flasks or colonies) was encountered in 34 cases (0.3 per cent). Analysis of the details of these cases allowed five major conclusions to be drawn: (1) Single cell abnormalities should not be taken as an indication of true fetal mosaicism. Only rarely will this interpretation prove to be incorrect. (2) Mosaicism involving multiple cells confined to a single flask should not be regarded as an indication of true fetal mosaicism. Only occasionally will this interpretation prove to be incorrect. (3) Mosaicism involving multiple cells distributed over more than one flask should be regarded as a strong indication of true fetal mosaicism. Sixty per cent will be confirmed by karyotype analysis of the fetus or infant. (4) Mosaicism of the XX/XY type is usually due to maternal cell contamination. Occasionally it can be a female fetus with XY cells from an unknown source. (5) The in situ or colony method of chromosome analysis has no clear advantage over the flask method for either the detection of true fetal mosaicism or for the ability to distinguish true mosaics from false positives.

Maternal uniparental isodisomy for chromosome 14 detected prenatally

“…They surmised that the risk of trisomy for any chromosome increases with maternal age and the trisomy rescue model of UPD probably applies to all chromosomes (Ledbetter and Engel, 1995). As level 3 (or true) trisomy mosaicism (Hsu et al, 1992) is recognized in at least 1 per cent of CVS (Vejerslev and Mikkelsen, 1989) and 0.1-0.3 per cent of amniocenteses (Hsu and Perlis, 1984;Worton and Stern, 1984), there is a substantial number of prenatal diagnostic cases in which the possibility of UPD should be considered.…”

3. Methods

“…6 Of the 20 cases of Level 3 mosaicism that had follow-up chromosomal tests, 12 (60 per cent) were confirmed and eight (40 per cent) were not confirmed.…”

Prevalence of Tetraploid Metaphases in Semidirect and Cultured Chorionic Villi

“…Furthermore, the prevalence of tetraploidy and tetraploidy/diploidy mosaicism in cultured amniotic fluid cells has been well documented [12,13]. However, a number of collaborative studies on chromosome mosaicism and pseudomosaicism in amniotic fluid cells did not mention diagnostic problems involving tetraploidy [14][15][16][17]. For chorionic villi, such experiences or basic data are not available.…”