Heterokaryotypic Pregnancy: Monozygotic Monochorionic Twins Discordant for Trisomy 13

Abstract

Background: The occurrence of a discordant chromosomal abnormality in monozygotic twins is an extremely rare condition. Case: We report the prenatal sonographic findings and cytogenetic studies in a monochorionic twin pregnancy discordant for severe fetal anomalies. Amniocenteses demonstrated heterokaryotypia for trisomy 13 in monozygotic twins. The pregnancy was managed conservatively, resulting in the delivery of discordant twins at 32 weeks. The structurally normal twin survived without sequelae, but the abnormal twin died shortly after delivery. Conclusions: This report adds to the literature the second known case of a spontaneously conceived monochorionic twin pregnancy discordant for trisomy 13 and highlights the necessity of sampling both fetuses in cases of monochorionic twins presenting with discordant structural anomalies.

Monozygotic twins discordant for trisomy 13

“…Previous literature reports include monozygous twins discordant for monosomy 21 2 in one case, trisomy 21 [3][4][5][6] in four cases and trisomy 13 7,8 in two cases.…”

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

“…Although no invasive antenatal testing was done, postnatal karyotyping confirmed trisomy 13 in the affected twin but normal chromosome complement in Twin B 2 . In at least seven of the subsequent nine cases [3][4][5][6][7][8][9] (details unavailable from Vojtěch et al, 11 amniocentesis of both sacs was performed (at gestational ages ranging from 13 + 6 to 23 weeks) and confirmed discordant karyotypes, with one twin affected by trisomy 13 and the other with normal karyotype. Uniquely in this series, our patient decided against amniocentesis prior to selective reduction: given the obvious severity of the affected twin's abnormalities, the result would not have altered her decision for selective termination but would have risked miscarriage of the unaffected twin.…”

“…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.…”

Monozygotic twins discordant for trisomy 13: counselling and management issues

“…5,6 There are only four reports of monochorionic twins discordant for trisomy 13. [6][7][8][9] The mechanism of occurrence of monozygotic twins has been discussed by various authors, 4,10 but little is known about the mechanisms underlying heterokaryotypic twinning. Parent of origin studies in our case indicated maternal origin of the trisomic chromosome.…”