Yao-Lung Chang1, Wu-Pei Yi2, An-Shine Chao1, Kuan-Ju Chen1, Po-Jen Cheng1, Tzu-Hao Wang3, Shuenn-Dyh Chang4. 1. Department of Obstetrics and Gynecology, Chang Gung Memorial Hospital, Linkou, College of Medicine, Chang Gung University, Taoyuan, Taiwan. 2. Cytogenetic Laboratory, Department of Obstetrics and Gynecology, Tao-Yuan Branch, Chang Gung Memorial Hospital, Taoyuan, Taiwan. 3. Department of Obstetrics and Gynecology, Chang Gung Memorial Hospital, Linkou, College of Medicine, Chang Gung University, Taoyuan, Taiwan; School of Traditional Chinese Medicine, College of Medicine, Chang Gung University, Taoyuan, Taiwan; Genomic Medicine Research Core Laboratory (GMRCL), Chang Gung Memorial Hospital, Taoyuan, Taiwan. 4. Department of Obstetrics and Gynecology, Chang Gung Memorial Hospital, Linkou, College of Medicine, Chang Gung University, Taoyuan, Taiwan; Cytogenetic Laboratory, Department of Obstetrics and Gynecology, Tao-Yuan Branch, Chang Gung Memorial Hospital, Taoyuan, Taiwan. Electronic address: gene@cgmh.org.tw.
Abstract
OBJECTIVE: To elucidate the etiologies of discordant trisomy 21 in monozygotic twin pregnancy. CASE REPORT: A monochorionic diamniotic twin pregnancy with hydrops and cleft lip (twin 1) found in one fetus presented at gestational age of 17 weeks. Amniotic fluid karyotyping showed nonmosaic trisomy 21 in twin 1 (47, XY, +21 [20]) and a normal karyotype in twin 2 (46, XY [20]). Short tandem repeat (STR) polymorphism markers revealed that the two fetuses were monozygotic, and the two chromosomes 21 were maternal isodisomy in the trisomy fetus. The chromosomal constitution of placentas in the territory of trisomy 21 cotwin was 47, XY, +21 [20] and was a mosaic 47, XY+21 [12]/46, XY [8] in the normal karyotyped twin. CONCLUSION: Our case of monozygotic twin with discordant trisomy 21 might start with a prezygotic maternal meiosis II non-disjunction error-caused trisomy 21 zygote, and after twinning, one remained trisomy 21, and the other twin underwent trisomy rescue and became a mosaic trisomy 21 in morula or early blastocyst stage before the formation of pre-embryo, which subsequently resulted in mosaic trisomy 21 of the placental tissue and normal chromosomal constitution of the fetus.
OBJECTIVE: To elucidate the etiologies of discordant trisomy 21 in monozygotic twin pregnancy. CASE REPORT: A monochorionic diamniotic twin pregnancy with hydrops and cleft lip (twin 1) found in one fetus presented at gestational age of 17 weeks. Amniotic fluid karyotyping showed nonmosaic trisomy 21 in twin 1 (47, XY, +21 [20]) and a normal karyotype in twin 2 (46, XY [20]). Short tandem repeat (STR) polymorphism markers revealed that the two fetuses were monozygotic, and the two chromosomes 21 were maternal isodisomy in the trisomy fetus. The chromosomal constitution of placentas in the territory of trisomy 21 cotwin was 47, XY, +21 [20] and was a mosaic 47, XY+21 [12]/46, XY [8] in the normal karyotyped twin. CONCLUSION: Our case of monozygotic twin with discordant trisomy 21 might start with a prezygotic maternal meiosis II non-disjunction error-caused trisomy 21 zygote, and after twinning, one remained trisomy 21, and the other twin underwent trisomy rescue and became a mosaic trisomy 21 in morula or early blastocyst stage before the formation of pre-embryo, which subsequently resulted in mosaic trisomy 21 of the placental tissue and normal chromosomal constitution of the fetus.