The triple X chromosome syndrome in childhood: recent empirical findings

This study addresses the issue of the relationship between intellectual ability and the X chromosome. It involves a sample of 11 girls ranging in age from 8 to 11 years who were identified at birth as having an extra X chromosome through a screening program for sex chromosome abnormalities. The purpose was to examine their performance on verbal, nonverbal, and memory tasks. The first study compared triple X girls with their normal siblings on standardized ability tasks. The results revealed markedly lower verbal skills in the extra X girls as well as a short-term memory deficit for sequentially ordered auditory information. The second study compared triple X subjects to age-matched normal girls on laboratory-based tasks of verbal and spatial information processing. The results revealed greater impairments with the verbal than the spatial task. The third study, which dealt with their recall abilities, involved comparing triple X girls with age- and ability-matched female controls on a wide variety of short-term memory tasks. The results showed that the triple X girls were markedly inferior in their performance on these tasks, indicating a rehearsal deficit, an inability to use list structures, and weaker language skills. The results are discussed in terms of the influence of various biological factors in mediating the deficits observed.