Brain morphometry in reading-disabled twins

Objective: To test for brain structure differences in reading disability (R D) by means of MRI-based morphometry. Background: Consensus is lacking on t he brain structural correlates of RD. The current study reports on a wider set of structures in the largest sample yet studied, controlling for age, g ender, IQ, and attention deficit hyperactivity disorder (ADHD), Methods: A case-control study was performed that was comprised of 75 individuals with RD (mean age, 17.43 +/- 4.29 years) and 22 control subjects without RD (mea n age, 18.69 +/- 3.75 years), each a single member of a twin pair. The two groups were similar in age, gender, and handedness, but differed in full-sc ale IQ (FSIQ), with the RD group having a lower mean FSIQ (101.8 +/- 9.9 ve rsus 118.3 +/- 10.3). Using three group-by-structure analyses of covariance , groups were compared in terms of volume tin cubic centimeters) of major n eocortical subdivisions, subcortical structures, and midsagittal areas tin square millimeters) of three subdivisions of the corpus callosum. Results: Controlling for age, gender, and IQ, the authors found a significant group- by-structure interaction for the major neocortical subdivisions (p = 0.002) , reflecting a different developmental pattern in the RD group, with the in sula and anterior superior neocortex being smaller and the retrocallosal co rtex being larger in the RD group. In contrast, they found no group main or interaction effects for the subcortical or callosal structures. The patter n of results was essentially the same in subjects without ADHD. Conclusions : Most brain structures do not differ in size in RD, but cortical developme nt is altered subtly. This study replicates in a larger sample previous fin dings of insular differences in RD and demonstrates further that those diff erences are not attributable to comorbid ADHD.