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The behavioural phenotype of women with Turner syndrome (X-monosomy, 45,X) is poorly understood, but includes reports of some social development anomalies. With this in mind, accuracy of direction of gaze detection was investigated in women with Turner syndrome. Two simple experimental tasks were used to test the prediction that the ability to ascertain gaze direction from face photographs showing small lateral angular gaze deviations would be impaired in this syndrome, compared with a control population of men and women. The prediction was confirmed and was found to affect both the detection of egocentric gaze from the eyes ('is the face looking at me?') and the detection of allocentric gaze, where the eyes in a photographed face inspected one of a number of locations of attention ('where is she looking?'). We suggest that dosage-sensitive X-linked genes contribute to the development of gaze-monitoring abilities.

Face recognition is often considered to be a modular (encapsulated) function. This annotation supports the proposal that faces are special, but suggests that their identification makes use of general-purpose cortical systems that are implicated in high-level vision and also in memory and learning more generally. These systems can be considered to function within two distinct cortical streams: a medial stream (for learning and salience of faces encountered) and a lateral stream (for distributed representations of visual properties and identities of faces). Function in the lateral stream, especially, may be critically dependent on the normal development of magnocellular vision. The relevance of face recognition anomalies in three developmental syndromes (Autism, Williams syndrome, and Turner syndrome) and the two-route model sketched above is considered.

We tested the cognitive abilities and educational attainments of 47 patients with a ring X chromosome, to evaluate the extent to which these variables correlated with failure of r(X) inactivation and with mosaicism. We found possession of a r(X) chromosome was associated with an increased risk of significant learning difficulties, and with associated behavioural maladjustment, compared with 45,X Turner females. Nearly a third had been educated outside mainstream schools. The proportion of cells in peripheral blood containing an inactivated r(X) chromosome was negatively correlated with nonverbal IQ. The parental origin of the normal chromosome did not appear to affect adjustment or abilities. In a minority of r(X) cases associated with mental retardation, there had been a failure to inactivate the ring, due to loss of the XIST locus. However, failure of X-inactivation was not necessarily associated with a severe phenotype. The degree of impairment in IQ depended on the size of the active ring, and hence was proportionate to the number of (as yet unidentified) genes whose functional disomy affected brain development and functioning.