Monozygotic twin discordant for Down syndrome: mos 47,XX,+21/46,XX and 46,XX |
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Authors: | Sun Ah Choi Jung Min Ko Choong Ho Shin Sei Won Yang Jin Sun Choi Sun Kyung Oh |
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Institution: | 1. 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 2. Institute of Reproductive Medicine and Population Medical Research Center, Seoul National University College of Medicine, Seoul, Republic of Korea
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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,+2199]/46,XX2]. 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. |
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