Brain volumes and surface morphology in monozygotic twins

Because healthy monozygotic twins share an identical genetic complement, they provide a unique opportunity to explore the genetic and environmental determinants of brain development. The purpose of this study was to evaluate the similarities between measures of cerebral and subcortical volumes and surface morphology in monozygotic twins compared with a matched control sample. Combinations of automated and manual methods were used to evaluate total brain volume, gray matter, white matter, ventricles and volumes of the frontal, temporal, parietal and occipital lobes. An artificial neural network algorithm was used to measure the cerebellum, thalamus, caudate and putamen. Measures of surface morphology included an index of gyral and sulcal curvature, surface area and cortical depth. The cerebral volume regions, including the gray matter, white matter and lobar volumes, were highly correlated within monozygotic twin pairs, with nearly all correlation coefficients >0.90. The cerebellum was also highly correlated (r = 0.99). Reasonably high correlations were found for the cortical depth (r = 0.84), caudate (r = 0.84), thalamus (r = 0.75) and putamen (r = 0.75). The surface measures, however, demonstrated the least correlation within twin pairs and thus are more prone to environmental influences. The high to moderate correlations between MZ twins compared with the matched controls highlights the role of heredity in both prenatal and postnatal neurodevelopment.