“…Imaging studies of adult twins have found genetic factors to account for 66-90% of total cerebral volume (Baare et al, 2001;Bartley, Jones, & Weinberger, 1997;Carmelli et al, 1998;Pfefferbaum, Sullivan, Swan, & Carmelli, 2000;Wright, Sham, Murray, Weinberger, & Bullmore, 2002) and similarly high heritabilities are reported for individual gray and white matter volumes (Baare et al, 2001;Posthuma et al, 2003), as well as mid-sagittal corpus callosum area (Pfefferbaum et al, 2000;Scamvougeras, Kigar, Jones, Weinberger, & Witelson, 2003). A single pediatric study of 34 MZ and 32 DZ pairs (some with and some without reading dis-ability) reported similar heritability of brain morphometric measures (Pennington et al, 2000).…”