Prenatal detection of chromosomal mosaicism

Abstract

A significant problem associated with cytogenetic prenatal diagnosis is distinguishing between true and pseudomosaicism. This becomes a diagnostic dilemma when fetal mosaicism corresponds with a known clinical entity. True mosaicism reportedly occurs with a frequency of 0.2 per cent and pseudomosaicism in 0.7 per cent to 2.7 per cent of cases. In the past 12 months, our laboratory has completed 522 fetal karyotypes. Nine cases were found to demonstrate mosaicism, 4 true mosaics (0.8 per cent) and 6 pseudomosaics (1.1 per cent). One case demonstrated both true and pseudomosaicism. In all cases of true mosaicism, the pregnancy was continued and karyotypes completed at birth. Our results demonstrate a danger of' rigid adherence to the criteria for true and pseudomosaicism in the examination of amniotic fluids. It is suggested that the criteria established for true and pseudomosaicism may not be valid when an aberrant cell line is found in a single flask and when that aberrant cell line is compatible with a known clinical entity due to a chromosome anomaly.

Mosaic trisomy 17 in amniotic fluid cells not confirmed in the newborn

“…The detection of mosaicism in routine cytogenetic analysis of amniotic fluid cells is a diagnostic problem, since owing to the diverse origin of these cells the aberrant cell line cannot be traced to the specific tissue of its origin (Najafzadeh et al, 1982;Cheung et al, 1990), so that the fetal phenotype cannot be accurately predicted. The aberrant cell line may have originated early, thus representing both the embryo proper and the extraembryonic tissue.…”

Five cases of prenatally diagnosed sex chromosome mosaicism

“…The detection of true mosaics in the routine of prenatal fetal karyotyping is a quite rare finding. Its incidence in amniotic fluid cell cultures is estimated to be from 0.1 to 0.76 per cent (Peakman et al, 1979;Golbus et al, 1979;B o d et al, 1979;Rudd, 1980;Hsu, 1980;Dill, 1980;Mikkelsen 1980;Webb et al, 1980;King et al, 1980;Najafzadeh et al, 1982). Mosaics were found in 5 out of 1322 (0.45 per cent) prenatal chromosome analyses performed in our laboratory from 1978 to 1982.…”

“…Our observation that the incidence of true mosaicism is 0.45 is similar to that reported in other studies on prenatal chromosome diagnosis (Peakman et al, 1979;Golbus et al, 1979;BouC et at., 1979;Rudd, 1980;Hsu, 1980;Dill, 1980;Mikkelsen, 1980;Webb et al, 1980;King et al, 1980;Najafzadeh et al, 1982). As can be seen in Table 2, the incidence ranged from 0.1 to 0.76 per cent.…”

A culture vessel for amniotic fluid cells allowing faster preparation of chromosome slides

“…by making a distinction between true fetal mosaicism and pseudomosaicism possible (Schmid, 1977: Peakman et a/., 1979Hecht et a/., 1981). Others, however, doubt the value of in situ techniques (Najafzadeh et al, 1982;Simpson et al, 1982). Amniotic cells migrate in culture (Alice 0.…”