We next analyzed heritability of cortical thickness in an expanded pediatric sample (214 MZ twins, 94 same-gender DZ twins, 64 siblings of twins, and 228 singletons, average age = 11.08, SD = 3.5; Lenroot, Schmitt, et al., 2007). Cortical thickness measurements were obtained and at each of 40,062 individual vertices using an automated method developed by colleagues at the Montreal Neurologic Institute (Lerch & Evans, 2005). Variance parameters were then estimated with structural equation modeling both for each individual vertex and for the average thickness in 54 separate cortical regions (Kabani, Le Goualher, MacDonald, & Evans, 2001).
