Issues arising from the prenatal diagnosis of some rare trisomy mosaics--the importance of cryptic fetal mosaicism.
OBJECTIVE
To add to the knowledge of fetal mosaicism, confined placental mosaicism (CPM), and uniparental disomy (UPD), in rare trisomies detected at prenatal diagnosis.


METHODS
The origin of rare trisomy mosaics, mostly (8/11) seen in amniocytes, was examined in 11 cases by follow-up karyotyping and the study of microsatellite inheritance.


RESULTS
Of the rare trisomies presented, three were mosaic trisomy 16 (two of which were CPM), and the remainder comprised single cases of mosaic trisomies of 8, 9, 10, 11, 12, 14, 5 and 15--the last two being CPM. Cases varied in parental derivation and meiotic versus post-zygotic origin but no case involved UPD. There was evidence for cryptic fetal mosaicism in three cases (5, 7, 11)--involving chromosomes 11, 14 and 16.


CONCLUSIONS
These cases contribute further data to phenotypes associated with rare trisomies and the relative influences on the phenotype of CPM, UPD and fetal mosaicism. From sparse published data, we estimate that approximately 10% of apparent CPM cases for a rare trisomy (i.e. aneuploid CVS, normal amniocytes) may actually be cryptic fetal mosaics undetected in cultured amniocytes. In many cases, this cryptic mosaicism may be of limited clinical significance, but in others, the associated phenotypic effects may be obvious. There is no general approach to resolve this issue; the finding of even a few similar aneuploid cells in different amniocyte culture vessels may be clinically significant. It may be useful to study such an amniocyte culture with FISH with the relevant centromeric probe. Careful follow-up is recommended, particularly for infants where apparent correction of autosomal trisomy has occurred.
Daniel
Art
A
Department of Cytogenetics, Western Sydney Genetics Program, The Children's Hospital at Westmead, NSW, Australia. artd@ch.edu.au
Wu
Zhanhe
Z
Darmanian
Artur
A
Malafiej
Paul
P
Tembe
Varsha
V
Peters
Greg
G
Kennedy
Craig
C
Adès
Lesley
L
D000328:Adult; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007621:Karyotyping; D008297:Male; D018895:Microsatellite Repeats / Q000235:genetics; D009030:Mosaicism / Q000196:embryology*; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D011256:Pregnancy Outcome; D011296:Prenatal Diagnosis; D012189:Retrospective Studies; D014314:Trisomy / Q000175:diagnosis* / Q000235:genetics*