Executive skills in Klinefelter's syndrome.

Executive skills are those involved in concept formation, problem solving, switching tasks, inhibiting inappropriate responses, initiating rapid and fluent responses, planning and sustained attention. Different patterns of disorder amongst these skills have been found in several developmental abnormalities including autism, attention deficit hyperactivity disorder (ADHD) and Turner's syndrome (TS). This study explored, for the first time, executive skills in children with Klinefelter's syndrome (KS), a sex chromosome abnormality in which there is one or more additional X-chromosomes. Intelligence in KS is normal but there is academic underachievement. A battery of executive tasks was administered, in a series of case studies, to three 10-year-old boys with KS and to controls matched for age, sex and intelligence. The results demonstrate that children with KS have impairments in executive skills. However, the pattern of impairment is task-specific. There is evidence from multiple tasks of impairment in inhibitory skills, for each case of KS. In contrast, concept formation, problem solving, task switching and speeded responding are normal. These results support theories that argue for distinct sub-components of executive skills within development that may develop relatively independently. The results have relevance for modelling both child and adult executive systems. They also confirm that an additional X-chromosome has highly selective effects upon the consequent cognitive phenotype seen in development.