Vein of Galen Aneurysmal Malformation in Monozygotic Twin.

BACKGROUND Vein of Galen aneurysmal malformation (VGAM) is a rare pediatric vascular malformation of the brain. Genetic backgrounds are not well elucidated. We report on a monozygotic twin with VGAM and his endovascular treatment, and the genetic analyses of the twins and their parents. CASE DESCRIPTION In a monochorionic, diamniotic pregnancy of a 28-year-old healthy woman, monozygotic twins were born by emergency caesarian section because of fetal distress of the smaller twin at 25 weeks' and 4 days' gestation. Although a postnatal cranial ultrasound failed to detect VGAM in the smaller twin, mild heart failure persisted. A brain magnetic resonance (MR) examination of this twin on day 82 revealed choroidal VGAM. The twin was treated successfully by two sessions of embolization at 6 and 8 months of age. An MR examination at 1 year showed minimal residual arteriovenous shunts. He developed normally similar to the normal co-twin, with a follow-up period of 1 year and 6 months. As for the affected twin, no germline mutation or copy number variations were identified in ENG, ALK1, SMAD4, BMPR2, PTEN, RASA1, KRIT1, Marcavernin, or PDCD10 through whole-exome sequencing (WES). CONCLUSION We have reported a rare combination of a monozygotic twin and VGAM and the successful endovascular treatment. Phenotypic discordance in monozygotic twins established early in embryogenesis could be attributable to environmental or epigenetic factors.