The aim of this study was to investigate the morphology of the corpus callosum (CC) in Tourette syndrome (TS) and attention deficit hyperactivity disorder (ADHD) to determine whether these conditions affect distinct regional differences. Seventy-seven children and adolescents, aged 6 to 16 years, comprised the four research groups--16 patients with TS, 21 patients with TS plus ADHD, 13 patients with ADHD, and 27 unaffected control subjects. A semiautomated, computer-assisted procedure was used to measure the total area, five subregions, centerline length, perimeter, and bending angle of the CC. MRI data were analyzed using several statistical methods, primarily two-tailed analysis of variance to test the effects of TS and ADHD status, while controlling for the influence of age, gender, and total intracranial area (an estimate of brain size). TS was associated with significant increases in the area of four of five subdivisions, the total area, and the perimeter of the CC. ADHD was associated with a significant decrease in the area of the rostral body. There were no interactions between TS and ADHD factors. These findings suggest that the area of the CC is larger in children with TS, and that this difference is independent of age, handedness, intracranial area, and the diagnosis of ADHD. Our findings support hypotheses that the neurobiologic mechanisms in TS and ADHD involve frontal/subcortical circuits.

The degree to which genetic factors influence human intelligence remains a matter of some controversy. However, there is little doubt that single gene mutations can significantly alter brain development and function. For example, mutations affecting the FMR1 gene cause the fragile X syndrome, the most prevalent known inherited cause of intellectual dysfunction. The most common mutation occurring in the FMR1 locus involves expansion of a trinucleotide (CGG)n repeat sequence within the promoter region of the gene. Between 6 and 54 repeats are typically observed in individuals from the general population. When > or = 200 CGG repeats are present, the expanded repeat sequence and an adjacent CpG island are usually hypermethylated, Aa phenomenon associated with transcriptional silencing of the gene and commonly referred to as the FMR1 full mutation. The intermediate range of repeats (approximately 50 to 200 CGGs), referred to as the premutation, is characterized by the absence of hypermethylation within the promoter region and normal phenotype. Some individuals have a combination of methylated and unmethylated alleles of differing size and are referred to as having mosaic status. Most males with the FMR1 full mutation function in the mentally retarded range of intelligence; in contrast, females with the FMR1 full mutation show a broader range of intelligence, from mental retardation to normal IQ.(ABSTRACT TRUNCATED AT 250 WORDS)

To determine the frequency of learning disabilities (LD) and describe the neuropsychological profile of children with Tourette's syndrome (TS) with and without attention deficit hyperactivity disorder (ADHD), we analyzed psychosocial, psychoeducational, and neuropsychological data from 65 children between the ages of 6 and 14 years selected from a larger study of LD. Three groups were formed: TS only, TS+ADHD, and TS +/- ADHD. The third group was composed of children whose ADHD status was not as strongly confirmed by the three different instruments used for ADHD diagnosis. From other (non-TS) research projects in the Center, a comparison group of 27 unaffected siblings who had no diagnosis of ADHD was formed. All children were unmedicated at the time of assessment and had the full set of data available for analysis. LDs were present in 23% of the total TS sample, but LD was not present in the TS-only group. All TS groups had scores at or below 1 SD from the mean on measures of choice reaction time, but the TS-only group was significantly poorer on a measure of executive function (letter word fluency). We discuss the implication of the finding in the TS-only group in terms of a slowing of linguistic productivity.