Is monochorionic twinning a risk factor for focal cortical dysgenesis?

Abstract

Objectives: Various genetic and acquired factors have been proposed as being etiologically important in cortical dysgenesis. It has been suggested that fetal, developmental abnormalities may be induced by transient, circulatory instability in monochorionic twinning due to feto-fetal transfusions. We report the discordant occurrence of a malformation of cortical development in monozygotic, monochorionic twins, and discuss the findings and possible pathogenetic mechanisms.

Material and methods: The twins were females, 30 years of age, one of them suffering from uncontrolled localization-related epilepsy. Neurological deficits or mental retardation were not present. Genetic analysis, brain MRI, and a neuropsychological test battery were carried out.

Results: DNA analysis verified monozygocity. MRI showed a unilateral grey matter heterotopion and a contralateral temporal arachnoid cyst in the affected twin. Neuro-psychological assessment revealed no corresponding focal cognitive deficits, but an overall slightly lowered performance in the affected twin.

Conclusion: Discordant affection of focal, cortical dysgenesis in monozygotic twins creates a particular opportunity to assess the consequences of such a disorder. The fact that only a mild generalized influence on cognitive functioning was demonstrated in this case, is possibly due to the plasticity of the fetal brain. According to current, obstetrical literature, the unique embryology of monochorionic twinning may predispose to vascular events in early fetal life. As ultrasound studies now indicate that a large proportion of pregnancies start out as twin products, we hypothesize that the "vanishing twin" syndrome and its potential hemodynamic hazard to the surviving fetus may be an etiological factor in malformations of cortical development, even in singletons.