title: Monozygotic twin discordant for Down syndrome: mos 47,XX,+21/46,XX and 46,XX.
abstract: Monozygotic twins, developed from a single zygote, are almost identical in clinical phenotype and concordant karyotypes. Monozygotic twins with discordant karyotypes are thought to be quite rare. Here, we report monochorionic-diamniotic twins discordant for Down syndrome. On findings of prenatal ultrasonography, nuchal translucency thickness was different between twins, and suggested that one of the twins was at high risk for having chromosomal abnormalities including Down syndrome. The twins were monochorionic-diamniotic; therefore, chorionic villi sampling of the common placenta was performed. The karyotype of the chorionic villi cells was 46,XX, and pregnancy was maintained. After delivery, dysmorphic clinical features suggesting Down syndrome were found in one of the twins, while the other twin showed a morphologically normal appearance. Karyotypes of peripheral blood leukocytes were repeatedly normal in the dysmorphic twin; however, the karyotype of skin fibroblasts from the dysmorphic twin indicated Down syndrome mosaicism; 47,XX,+21[99]/46,XX[2]. The karyotype of skin fibroblasts from the morphologically normal twin was 46,XX. Monozygosity of the twins was confirmed by a short tandem repeat analysis using 16 polymorphic markers. A mitotic nondisjunction followed by the twinning would explain the discordant karyotypes between monozygotic twins.
authors.affiliation: Department of Pediatrics, Seoul National University Children's Hospital, Seoul National University College of Medicine, 101 Daehak-ro, Jongno-gu, Seoul 110-769, Republic of Korea.
authors.forename: Sun Ah
authors.initials: SA
authors.lastname: Choi
authors.forename: Jung Min
authors.initials: JM
authors.lastname: Ko
authors.forename: Choong Ho
authors.initials: CH
authors.lastname: Shin
authors.forename: Sei Won
authors.initials: SW
authors.lastname: Yang
authors.forename: Jin Sun
authors.initials: JS
authors.lastname: Choi
authors.forename: Sun Kyung
authors.initials: SK
authors.lastname: Oh
mesh_terms: D002869:Chromosome Aberrations; D004200:Diseases in Twins / Q000175:diagnosis / Q000235:genetics*; D004314:Down Syndrome / Q000175:diagnosis / Q000235:genetics*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007621:Karyotyping; D009030:Mosaicism; D011247:Pregnancy; D011296:Prenatal Diagnosis; D014430:Twins, Monozygotic / Q000235:genetics*; D016216:Ultrasonography, Prenatal
references.citation: Am J Med Genet A. 2008 Aug 15;146A(16):2086-93
references.pmid: 18627064
references.citation: Early Hum Dev. 2001 Sep;64(2):105-17
references.pmid: 11440823
references.citation: Eur J Pediatr. 2004 Oct;163(10):634-5
references.pmid: 15290260
references.citation: Eur J Med Genet. 2012 Aug-Sep;55(8-9):480-4
references.pmid: 22677035
references.citation: Am J Med Genet A. 2005 Jun 1;135(2):190-4
references.pmid: 15832362
references.citation: Am J Med Genet C Semin Med Genet. 2009 May 15;151C(2):110-27
references.pmid: 19363805
references.citation: J Med Genet. 1994 Sep;31(9):694-701
references.pmid: 7815438
references.citation: J Pediatr. 2004 Sep;145(3):406-8
references.pmid: 15343200
references.citation: Am J Med Genet. 1996 Jan 22;61(3):216-28
references.pmid: 8741866
references.citation: Hum Reprod. 2006 Aug;21(8):2175-9
references.pmid: 16772284
references.citation: Am J Med Genet. 1982 Feb;11(2):143-6
references.pmid: 6461252
references.citation: BMJ. 1999 Mar 27;318(7187):856-7
references.pmid: 10092267