Neurocognitive characteristics of individuals with resistance to thyroid hormone: comparisons with individuals with attention-deficit hyperactivity disorder.

Previous studies have demonstrated an association between resistance to thyroid hormone (RTH) and attention-deficit hyperactivity disorder (ADHD). To determine if the neurocognitive characteristics in individuals with RTH are similar to those observed in ADHD, 12 children with RTH from 7 families were matched to 12 children with ADHD without RTH. Subjects were administered standardized intellectual, developmental, and school achievement tests. Parent and teacher ratings of children's hyperactivity and attention were similar for both groups, as were measures of attention, impulsivity, and verbal IQ. Children with RTH displayed lower nonverbal intelligence (performance IQ = 85) and academic achievement (> 1-2 SD below the mean) when compared with those with ADHD only (performance IQ = 99; achievement within 2 SD). Although children with RTH have behavioral characteristics similar to those with ADHD, their significantly weaker abilities of perceptual-organization and lower school achievement suggest a more severe neurobehavioral impairment than ADHD.