HEAD CIRCUMFERENCE AND IQ OF CHILDREN WITH SEX-CHROMOSOME ABNORMALITIES

At all ages XXX girls had significantly smaller head circumferences th an control girls. Their IQ deficit was 24 points and IQ at age seven c orrelated significantly with head circumference at birth. In XXY boys, head circumference was significantly reduced at birth and up to nine years of age. The XXY boys' IQ deficit was 22 points, but IQ did not c orrelate with head circumference, as reductions in the two parameters did not always occur in tandem. The ratio of height-to-head circumfere nce differed most in this group and could be useful in clinical recogn ition of this condition. XYY boys' head size did not differ from contr ols, despite their greater height, lower IQ scores indicating an adver se effect of an additional Y chromosome on brain development. The majo r factor affecting IQ outcome in the cohort was abnormal karyotype, wi th smaller effects from social class and head growth.