Heterokaryotypic pregnancy:
monozygotic monochorionic twins
discordant for trisomy 13
Email: [email protected]
Spacek R1, Pannova J1, Matura D1,2, Simetka O1,2
1. Department of Obstetrics and Gynecology, University Hospital Ostrava, Ostrava, Czech Republic
2. Department of Surgical Studies, University of Ostrava, Ostrava, Czech Republic
Objectives: To describe a rare case of heterokaryotypic monozygotic twins – monochorionic diamniotic – discordant for trisomy 13.
Methods: Case report
Results: A 23 years old primiparous women with spontaneous monochorionic twin pregnancy underwent first trimester screening in our
department which was negative for trisomy 21, 18 and 13. One fetus had no structural abnormalities, while in the other one
gastroschisis was detected. Due to this finding she underwent genetic consultation and amniocentesis was performed. The result of the
karyotyping was 47XY + 13 for the fetus with gastroschisis (fetus A) and 46XY for the structurally normal fetus (fetus B). Monozygotic
pregnancy was confirmed. During the 16th week scan another structural abnormality in fetus A was detected - right sided palate and lip
cleft and in 20th week left sided hydronephrosis and megaureter was found. Due to the pathological finding the patient opted for
selective reduction of the fetus A which was performed at 21st week of pregnancy in Fetal Medicine Center, Institute for the Care of
Mother and Child in Prague, Czech Republic using bipolar cord oclusion. The intervention was performed without any complication.
The pregnancy was then followed at our instution until week 36 when the healthy fetus was delivered by cesarean section for
intrauterine growth restriction, oligohydramnion and breech presentation. The measurements of the baby boy were 2400 grams and 44
centimeters, Apgar score 9-9-10. The boy had no structural abnormalities.
flat face
gastroschisis
right sided palate and lip cleft
gastroschisis 3D
Conclusion: Heterokaryotypic monochorionic twins are very rare and karyotypic difference is caused by asymmetric X-chromosome
inactivation and differential gene imprinting post-zygotic mitotic errors such as nondisjunction and anaphase lag. The most common
cause of this is nondisjunction of homologous chromosomes. According to the phase of zygote formation in which the nondisjunction
occurs, it is determined whether genetic abnormalities occur in all fetuses or in only one fetus. In other words, one fetus will have
genetic abnormalities but another fetus will be normal if the nondisjunction occurs after zygote formation is completed.1,2,3 The incidence
is not described in the literature. Our suspicion for this anomaly begun with discordant ultrasound findings during first trimester
screening. Diagnosis was confirmed by amniocentesis.
Discordant ultrasound findings in case of monozygotic twins should lead to suspicion for heterokaryotypic pregnancy.
References:
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Twin Pregnancy with Discordant for Turner Syndrome. Korean J Perinatol. 2014 Dec;25(4):292-296.
2. Nobili E, Paramasivam G, Kumar S. Outcome following selective fetal reduction in monochorionic and dichorionic twin pregnancies discordant for structural, chromosomal and genetic
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