Heritability of FA and RD in the whole WM was higher in neonates (FA=60% and RD=53%)(Y. Chen et al. 2009; Geng et al. 2012) compared to children (for FA~ 54%) (Brouwer et al. 2010; Brouwer et al. 2012; Chiang et al. 2011) and adults (FA=52% and RD=37%) (Kochunov et al. 2010). Likewise, AD heritability was moderate (57%) in neonates (Geng et al. 2012), but lower (33–46%) in children (Brouwer et al. 2010; Brouwer et al. 2012) and not significant in adults (Kochunov et al. 2010). AD reflects the axonal organization and is often used to assess for possible injury to fiber bundles (Budde et al. 2007), and therefore may provide a sensitive measure of environmental influences in the brain during development.
