Monozygotic twins discordant for trisomy 4: A Case Report
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A 32-year-old woman who had achieved her first pregnancy by natural conception. A first trimester ultrasound examination revealed a MC-DA twin pregnancy with one foetus (Twin A) with a large cystic hygroma, while the other foetus (Twin B) was normal. An amniotic fluid sample from both sacs were obtained. Rapid detection for aneuploidies by fluorescent in situ hybridisation (FISH) analysis showed a normal result for chromosomes 13, 18, 21 and sex chromosomes in both foetuses.

However, discordant karyotypes were obtained: the karyotype of Twin A revealed a full trisomy 4 (47, XX, þ4) obtained after the study of 20 metaphases from two different cell cultures, whereas the karyotype of Twin B was normal (46, XX). The morphological sonographic examination at 20 weeks
of gestation identified an affected female foetus (twin A) with foetal structural anomalies consistent with a single umbilical artery, intrauterine growth retardation, microcephaly, agenesis of the corpus callosum, bilateral ventriculomegaly, cerebellum hypoplasia, spina bifida, characteristic thumb anomalies (aplasia), retrognatia, clubfeet, absence of stomach bubble, suspected left diaphragmatic hernia with hypoplastic lungs, apparently normal right shifted heart and left kidney agenesis. Twin B had a normal female ultrasound appearance. Selective twin foeticide by cord occlusion of the abnormal foetus versus expectant management were offered.

The parents chose the second option. Because of a breech presentation, a spontaneous preterm labour caesarean section was performed at 33 þ 5 weeks of gestation. Twin A’s birth weight was 995 g (<(–)2.5 SD) the Apgar score was 1/1/1 at 1, 5 and 10 min, and Twin A died 1 h after birth. Twin B was a healthy liveborn female weighing 1950 g. After delivery, macroscopic examination confirmed a single 250 g monochorionic placenta. Clinical examination of newborn.A demonstrated hypotonia, hypertelorism, short palpebral fissures, broad and bifid spina, retrognathia, a hypoplastic proximal phalanx of the right thumb and a pectus carinatum.