MOSAIC TRISOMY 9 AT AMNIOCENTESIS: PRENATAL DIAGNOSIS AND MOLECULAR GENETIC ANALYSES

Objective To present prenatal diagnosis and molecular genetic analyses of mosaic trisomy 9 Materials, Methods and 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 chromo some 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 Conclusion 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 [Taiwan J Obstet Gynecol 2010,49(3) 341-350]