The only quantitative neuroimaging studies published thus far in children and adolescents with 49,XXY have been from the Sex Chromosome Variations Study being carried out within the National Institute of Mental Health [Giedd et al., 2007]. Forty-two nonmosaic 49,XXY subjects were recruited nationally with assistance of parental advocacy and support groups and compared with an age and sex matched group of 87 healthy controls. All 49,XXY boys over the age of 14 were receiving testosterone supplementation, none of the group under 12 years were receiving testosterone supplementation, and of the remainder half were receiving testosterone supplementation, and half were not receiving testosterone supplementation. IQ was significantly lower in the 49,XXY group (95.2 ± 17.1 vs. 120.3 ± 11.3, P < 0.0001), although still within the normal range of intelligence, whereas the control group was higher than expected for population norms. Nonverbal IQ was less impaired than verbal IQ.
