Etiology of neuroanatomical correlates of reading disability

The heritable nature of reading disability has been well documented (DeFrie s & Alarcon, 1996), and possible abnormalities of brain structures have bee n associated with the disorder (Filipek, 1995). However, the etiology of in dividual differences in morphological brain measures has not been examined extensively. The purpose of this study was to apply behavioral genetic meth ods to assess the etiology of individual differences in neuroanatomical str uctures. Measures of reading performance, cognitive ability, and magnetic r esonance imaging scans were obtained from 25 monozygotic (MZ) and 23 same-s ex dizygotic (DZ) twin pairs with reading disability, and 9 MZ and 9 DZ con trol twin pairs participating in the Colorado Learning Dis-abilities Resear ch Center. Results obtained from multiple regression analyses (DeFries & Fu lker, 1985, 1988) of these twin data indicated that individual differences in the size of most cortical and subcortical structures were largely due to heritable influences. Moreover, estimates of heritability did not change a ppreciably after controlling for IQ and total brain size.