Mosaicism in amniotic fluid cell cultures: Classification and significance

Abstract

The last decade has witnessed increasing application of human cytogenetic technology to prenatal chromosome analysis. However, unlike the rather uniform peripheral blood T-lymphocyte system which has provided most of our experience in human cytogenetics, long-term amniotic-fluid cell cultures display extreme cellular heterogeneity and disproportionate growth of certain cell types as a consequence of clonal amplification. When they enter cell culture, many of these cells are approaching the terminal stages of their respective, life spans and may have accumulated chromosomal aberrations. Concern about the possibility of true fetal mosaicism seems warranted chiefly in situations were multiple colonies display potentially viable aberrations. Clonal analysis, preferably of multiple clonal types, and attention to details of clonal morphology are likely to minimize diagnostic errors and undue apprehension resulting from mosaicism in amniotic-fluid cell cultures.

Autosomal mosaicism in amniotic fluid cells from a twin pregnancy

“…ism can be difficult, since the mosaic cells could represent true mosaicism of the fetus, "pseudomosaicism" of the amniotic membranes, or culture artifact. In some cases, in situ clonal analysis of amniotic fluid cultures may be useful in the interpretation of mosaicism [6].The finding of mosaicism in the prenatal diagnosis of a twin pregnancy has, to our knowledge, not been previously reported. We report a case that exemplifies the difficulties encountered when chromosomal mosaicism is found in one of two amniotic fluid specimens from a twin pregnancy.…”

“…Further details of this technique have been published [lo]. The advantages of in situ techniques in interpreting amniotic fluid cell cultures have been discussed [6].From the first specimen, 25 cells were analyzed from the four culture flasks. All of those cells had a normal female chromosome constitution (46,XX).…”

Chorion in culture

“…This result is significantly different from that obtained for other foetal tissues and suggests a tendency for single colonies in chorion to develop non-modal cells, which in the extreme case of clonal amplification could be interpreted as mosaicism. Hoehn et al (1978) also suggest that extra-foetal tissues have a relatively high background level of cytogenetic aberration. Chorion can be considered comparatively aged by the time it is cultured and composed of cells which are nearing the end of their destined lifespan.…”

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].…”