The size of the corpus callosum (CC) in Tourette’s syndrome (TS) and ADHD was determined by analysis of MRI data in 77 children and adolescents, aged 6 to 16 years, including 27 controls, at the Kennedy Krieger Institute, Johns Hopkins University School of Medicine, Baltimore, MD. TS patients had significant increases in 4 of 5 subregions (splenium, isthmus/posterior body, mid-body, and rostral body), the total area, and the perimeter of the CC. ADHD was associated with a significant decrease in the rostral body size. Inspection of subgroup means demonstrated a statistical independence of the effects of ADHD versus effects of TS on CC size. The larger CC in TS was independent of age, handedness, intracranial area, and the association of ADHD. 
COMMENT. The authors comment that TS and ADHD may result from distinct neurodevelopmental processes, and the three syndrome groups, comprising TS only, ADHD, and TS + ADHD, may represent different degrees of expression of the same gene. In addition to genetic transmission, environmental influences include prenatal factors, anabolic steroids, and antineural antibodies induced by streptococcal infection. (Singer HS, in Progress in Pediatric Neurology II, 1994, pp 227-231).