Genetic regulation of regional microstructure of the corpus callosum in late life

In order to identify brain structural phenotypes that remain under signific ant genetic control in late adulthood, we examined the heritability of corp us callosum macrostructure (i.e. size) using MRI and microstructure (e.g. m yelin) using diffusion tensor imaging in 15 monozygotic and 18 dizygotic tw in pairs of elderly men. The relative proportion of genetic to environmenta l influences varied considerably by region and structural type and was 5:1 for callosal macrostructure, 3:1 for splenium microstructure, and 1:1 for g enu microstructure. This is the first in vivo identification of quantifiabl e phenotypes of brain white matter microstructure and demonstrates signific ant and differential genetic regulation in old age, with anterior interhemi spheric connecting pathways more susceptible than posterior pathways to env ironmental influences. NeuroReport 12:1677-1681. (C) 2001 Lippincott Willia ms & Wilkins.