In the last two decades, neuroimaging studies revealed the importance of WM in several psychiatric and neurodegenerative disorders. Although genetics may play a role in WM integrity during brain development, heritability in WM integrity has not yet been examined extensively across the lifespan. Most studies to date involved adults since the peak maturation of the WM occurs at the age range of 25–40 years. However, three longitudinal twin studies examined the heritability of WM integrity with age in infants (Y. Chen et al. 2009) and adolescents (Chiang et al. 2011; Brouwer et al. 2012), while two other studies evaluated heritability cross-sectionally in neonates at 40 days post birth (Geng et al. 2012) and at 9 years of age (Brouwer et al. 2010).
