title: Misinterpretation of trisomy 18 as a pseudomosaicism at third-trimester amniocentesis of a child with a mosaic 46,XY/47,XY, +3/48,XXY, +18 karyotype.
abstract: False-negative trisomy 18 has been reported after chorionic villus sampling, but not after amniocentesis. We describe a double aneuploidy in cultured amniocytes that was initially misinterpreted as a pseudomosaicism. A patient was referred at 31 weeks of gestation because of fetal anomalies at ultrasound examination. Karyotyping of amniocytes showed a 47,XY, +3 karyotype in 61 clones and a 48,XXY, +18 karyotype in one clone. The latter was interpreted as a pseudomosaicism, the more since a second amniocentesis revealed only cells with a 47,XY, +3 karyotype. At 36 weeks gestational age, a boy was born with congenital anomalies suggestive of trisomy 18. A blood culture showed a 48,XXY, +18 karyotype, while in fibroblasts a 47,XY, + 3/48,XXY, +18 mosaicism was found. Umbilical cord and bladder epithelial tissue also revealed normal 46,XY cells, besides the aneuploid cells. Therefore, the child proper had a 46,XY/47,XY, +3/48,XXY, +18 mosaicism with the clinical symptoms of trisomy 18. To the best of our knowledge, this is the first report of a false-negative result of trisomy 18 together with three sex chromosomes after amniocentesis.
authors.affiliation: Department of Human Genetics, University Hospital Nijmegen, The Netherlands.
authors.forename: C M
authors.initials: CM
authors.lastname: van Ravenswaaij-Arts
authors.forename: J H
authors.initials: JH
authors.lastname: Tuerlings
authors.forename: A F
authors.initials: AF
authors.lastname: Van Heyst
authors.forename: J G
authors.initials: JG
authors.lastname: Nijhuis
authors.forename: J
authors.initials: J
authors.lastname: Niehof
authors.forename: D F
authors.initials: DF
authors.lastname: Smeets
mesh_terms: D000015:Abnormalities, Multiple / Q000175:diagnosis; D000649:Amniocentesis; D002869:Chromosome Aberrations / Q000175:diagnosis*; D025063:Chromosome Disorders; D002887:Chromosomes, Human, Pair 18; D005189:False Positive Reactions; D005260:Female; D005315:Fetal Diseases / Q000175:diagnosis; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D009030:Mosaicism / Q000175:diagnosis*; D011247:Pregnancy; D011263:Pregnancy Trimester, Third; D014314:Trisomy