Mosaic trisomy 9 at amniocentesis: prenatal diagnosis and molecular genetic analyses.
OBJECTIVE
To present prenatal diagnosis and molecular genetic analyses of mosaic trisomy 9.


RESULTS
A 35-year-old woman, gravida 3, para 1, underwent amniocentesis at 17 weeks of gestation because of her advanced maternal age. Amniocentesis revealed a karyotype of 47,XX,+9[3]/46,XX[6]. Repeat amniocentesis at 19 weeks of gestation revealed a karyotype of 47,XX,+9[6]/46,XX[19]. At 22 weeks of gestation, she was referred to a tertiary medical center for genetic counseling, and amniocentesis revealed a karyotype of 47,XX,+9[2]/46,XX[22]. Array comparative genomic hybridization analysis of uncultured amniocytes revealed no genomic imbalance in chromosome 9. However, interphase fluorescence in situ hybridization analysis of uncultured amniocytes showed that nine (18%) of 50 cells were trisomic for chromosome 9. Polymorphic DNA marker analyses also revealed a diallelic pattern with unequal biparental inheritance of chromosome 9 and a dosage ratio of 1:18 (paternal allele:maternal allele) in the uncultured amniocytes and a dosage ratio of 1:36 in the cultured amniocytes, indicating that the euploid cell line had maternal uniparental isodisomy for chromosome 9. Level II ultrasound demonstrated bilateral ventriculomegaly. The pregnancy was subsequently terminated, and a malformed fetus was delivered. Postnatal cytogenetic and polymorphic DNA marker analyses of the fetal and extraembryonic tissues confirmed the prenatal diagnosis.


CONCLUSIONS
Mosaic trisomy 9 carries a high risk of fetal abnormalities warranting detailed sonographic investigation of congenital malformations. Mosaic trisomy 9 can be associated with maternal uniparental disomy for chromosome 9 in euploid cell lines. Array comparative genomic hybridization is limited for the detection of low-level mosaicism.
Department of Obstetrics and Gynecology, Mackay Memorial Hospital, Pan-Chiao, Taiwan. cpc_mmh@yahoo.com
Chih-Ping
CP
Chen
Hsien-Ming
HM
Lin
Yi-Ning
YN
Su
Schu-Rern
SR
Chern
Fuu-Jen
FJ
Tsai
Pei-Chen
PC
Wu
Chen-Chi
CC
Lee
Yu-Ting
YT
Chen
Meng-Shan
MS
Lee
Chen-Wen
CW
Pan
Wayseen
W
Wang
D000015:Abnormalities, Multiple / Q000175:diagnosis / Q000235:genetics; D000028:Abortion, Induced; D000328:Adult; D000649:Amniocentesis; D002869:Chromosome Aberrations; D002899:Chromosomes, Human, Pair 9 / Q000235:genetics; D005260:Female; D006801:Humans; D009030:Mosaicism; D011247:Pregnancy; D014314:Trisomy / Q000175:diagnosis / Q000235:genetics; D024182:Uniparental Disomy / Q000175:diagnosis / Q000235:genetics