Discordant phenotypic outcomes in monozygotic twins conceived via IVF: A case report involving Hirschsprung's disease, tricuspid and pulmonary atresia, and orofacial clefts without detectable genetic mutation.

This report concerns the incidental finding of discordant congenital anomalies in twins diagnosed as monozygotic in a private, academically-affiliated fertility center in the United States. A 40-year-old woman conceived monozygotic dichorionic twins via in vitro fertilization (IVF). One twin presented with multiple congenital anomalies, including tricuspid and pulmonary atresia, cleft lip/palate, Hirschsprung's disease, facial skin tags, and a benign ocular tumor, while the other twin presented none of those abnormalities and appeared entirely healthy. Genetic testing, including amniocentesis and whole-exome sequencing, confirmed no identifiable mutations. This case emphasizes the potential role of postzygotic mosaicism, epigenetic dysregulation, and/or environmental disruption of neural crest-derived development, highlighting the complexity of embryologic development.