Concordant Open Neural Tube Defects in a Monochorionic Twin Pair of a Dichorionic-Triamniotic Triplet Gestation.

Introduction Myelomeningocele (MMC) is a type of open neural defect that involves exposure of the meninges and neural elements. There are fewer than 30 cases of twins with concordant MMCs reported in the literature. We discuss a case of dichorionic-triamniotic triplets in which the monochorionic-diamniotic pair was diagnosed antenatally with MMC. Case Summary The mother presented for routine prenatal care at 11 weeks of gestation as a 31-year-old G5P4003. A limited ultrasound at 18 weeks of gestation confirmed her estimated due date, and three viable fetuses were observed. She was found to have dichorionic-triamniotic triplets with Triplet A and Triplet B sharing a placenta. A detailed anatomic survey demonstrated MMC of Triplet B at L4-S2 and a suspected open neural tube defect in Triplet A. Triplet C had no apparent defects on ultrasound. MMC of Triplets A and B was confirmed postnatally. Chromosome microarray analyses for the triplets were normal. Discussion Most cases of MMC in monozygotic twins are nonconcordant, and the role of genetics remains ambiguous. Our case suggests a possible shared genetic etiology. Future studies may investigate the potential for a single-gene mutation driving the development of MMC.