Mosaic Trisomy 7 at Amniocentesis: Prenatal Diagnosis and Molecular Genetic Analyses

Objective To present prenatal diagnosis and molecular genetic analyses of mosaic trisomy 7 Materials, Methods and Results A 38 year old primigravid woman underwent amniocentesis at 19 weeks of gestation because of her advanced maternal age Amniocentesis revealed a karyotype of 47,XY,+7[26]/ 46 XY[161 Repeated amniocentesis at 21 weeks of gestation revealed a karyotype of 47,XY,+7[20]/46,XY[17] Simultaneous cordocentesis revealed a karyotype of 46,XY in 100/100 cultured lymphocytes Polymorphic DNA marker analyses of uncultured amniocytes and cord blood revealed a diallelic pattern with seemingly equal biparental inheritance of chromosome 7 Repeated cordocentesis and chorionic villus sampling at 23 weeks of gestation revealed a karyotype of 47,XY,+7[2]/46,XY[661 in cord blood and a karyotype of 47,XY,+7 in 24/24 cultured chorionic villi cells Level II ultrasonography was normal At 40 weeks of gestation, a 2,708 g normal male baby was delivered The peripheral blood had a karyotype of 46,XY in 100/ 100 lymphocytes Molecular analyses of placenta, urine, buccal swab, and peripheral blood revealed a diallelic pattern and seemingly equal biparental inheritance of chromosome 7 in all tissues At 3 months of age, he manifested hypopigmented skin and inguinal hernia, but showed normal growth and mental development Fluorescence in situ hybridization analysis of inguinal hernia sac tissue revealed that 19/100( 19%) of nuclei had three chromosome 7 signals Conclusion Mosaic trisomy 7 at amniocentesis may be derived from a cell culture artifact from an undetected low level of trisomy 7 mosaicism in uncultured amniocytes and can be associated with favorable fetal outcome if the blood has a normal karyotype or a very low level of mosaicism and if uniparental disomy for chromosome 7 is excluded