Monozygotic Twins Discordant for Trisomy 13; A Case of Trisomic Rescue Supporting the Continued Need for First Trimester Ultrasound

Abstract

Monozygotic twins with discordant karyotypes for trisomy 13 are rare. We report a case of a spontaneously conceived pregnancy who presented with first trimester ultrasound finding of umbilical cord cyst and increased nuchal translucency in Twin A and no abnormalities in Twin B. Amniocentesis revealed 47,XY,+13 karyotype in Twin A and 46,XY karyotype in Twin B. Selective fetal reduction was performed for Twin A. Twin B was delivered at 32 weeks gestation with normal phenotype. Peripheral blood karyotype revealed 15% mosaicism for trisomy 13 and skin fibroblast revealed 46,XY karyotype. The surviving twin will be monitored for potential complication of uniparental disomy 13 and mosaic trisomy 13. This case reinforces the need for early ultrasound and nuchal translucency measurements, especially in twin gestations.

Monochorionic twins discordant for trisomy 13: A case report, systematic literature search and synthesis of available evidence

“…10 In the other six cases, the unaffected cotwin survived,gestational age at delivery ranged from 32 + 2 to 40 weeks, with only one unaffected cotwin delivered before 36 weeks. 6 Three cases were managed expectantly (one only diagnosed at 25 weeks so termination not offered, 4 one case from Chile where termination is illegal under all circumstances, 8 and one in which termination was offered but declined. 7 One of these resulted in loss of both twins as discussed above, 4 the other two both resulted in delivery at 32 weeks with neonatal death of the affected twin and survival of the unaffected cotwin.…”

“…Spontaneous "rescue" chromosome loss in an initially trisomic zygote. 3,[5][6][7][8] Both mitotic error and trisomic rescue can give rise to uniparental disomy and mosaicism. 3,[5][6][7][8]10 Uniparental disomy may lead to phenotypic abnormalities if the chromosome involved has a high proportion of imprinted genes, but as noted by Ramsey et al, four cases of paternal and one case of maternal uniparental disomy for chromosome 13 have been reported, all with normal phenotypes.…”

“…In the case of laser cord coagulation, the unaffected cotwin subsequently died at 18 + 4 10 . In the other six cases, the unaffected cotwin survived,gestational age at delivery ranged from 32 + 2 to 40 weeks, with only one unaffected cotwin delivered before 36 weeks 6 …”

“…These include: Dizygosity, in which monochorionic twins are assumed to be monozygotic but in fact result from dizygotic conception with early fusion of the outer cell mass 5,7 Mitotic error during an early postzygotic cell division, leading to aneuploidy in that cell lineage 3,5‐7,9 Spontaneous “rescue” chromosome loss in an initially trisomic zygote 3,5‐8 …”

“…Five were excluded, due to: duplicates (1); articles describing monochorionic twins with discordant structural anomalies but identical karyotypes (2); and articles describing discordant aneuploidies other than trisomy 13 (2). Nine remaining articles [3][4][5][6][7][8][9][10][11] were selected for full-text review, all of which were included in the final analysis. These are summarized in Table 1.…”