Heteropagus conjoined twins due to fusion of two embryos: Report and review

Abstract

We report on a case of conjoined twinning (CT) consistent with fusion of two embryos followed by resorption of the cranial half of one of them, resulting in a normal male baby with the lower half of a male parasitic twin fused to his chest. Fluorescent in situ hybridization (FISH) studies suggested that the parasitic twin was male, and DNA typing studies demonstrated dizygosity. Although incomplete fission is the usual explanation for conjoined twins, the unusual perpendicular orientation of the parasite to the autosite supports a mechanism observed in mares in which early fusion of two embryos is followed by resorption due to compromised embryonic polarity.

Case Report on “Conjoined Embryos”

“…Therefore, it follows to hypothesize that in conjoined twinning the twinning event occurs at a later time during development than the twinning event that leads to two separate mono-amniotic twins. Most DNA typing studies of conjoined twinning demonstrated mono-zygosity in support of the fission theory, however, an exceptional case was reported by Logrono et al 5 where DNA typing demonstrated di-zygosity rather thanmono-zygosity.…”

“…The fact that conjoined twins are mostly monozygotic could be explained by the fact that monozygotic twin embryos are more likely to be in closer proximity than dizygotic twin embryos and as such incidences of conjoin twining is more likely in the monozygotic, however, it is not entirely impossible to occur in dizygotic twin embryos as reported in a study mentioned earlier by Logrono et al 5 It could also be postulated that mirror-image twinning is more prevalent in conjoined twinning because they are likely to be positioned closely and as such the incidence of mirror image twins would be higher in conjoined twinning.…”

“…Fusion theory of conjoined twinning: Another theory regarding conjoined twinning is known as the "fusion" or "collision" theory. [5][6][7][8] This implies that stem cells from one twin adhere to like stem cells from the other twin, fusing together and developing conjoined. Here also, there is no identified explanation for why this would happen.…”

Prenatal diagnosis of conjoined twins: Four cases in a prenatal center

“…The sonographic diagnosis of conjoined twins was first reported by Wilson et al (6). Conjoined twins have been diagnosed in the first trimester with both transabdominal and transvaginal sonography (10,11). According to Hill (12), the earliest prenatal suspicion of conjoined twins can arise at 7 weeks gestation.…”

Antenatally Diagnosed Epigastric Heteropagus Twin: Case Report

“…10 Heteropagusun ortaya çıkışında bir başka görüş de dizigotik ikizlerin erken füzyonu sonucu geliştiği şeklindedir. 11 Bu konuda yapılacak moleküler ve genetik çalışmalar henüz tam olarak ortaya konmamış etiyolojinin aydınlanmasında yol gösterici olacaktır.…”