Turner's syndrome is a sporadic disorder of human females in which all or part of one X chromosome is deleted. Intelligence is usually normal but social adjustment problems are common. Here we report a study of 80 females with Turner's syndrome and a single X chromosome, in 55 of which the X was maternally derived (45,X[m]) and in 25 it was of paternal origin (45,X[p]). Members of the 45,X[p] group were significantly better adjusted, with superior verbal and higher-order executive function skills, which mediate social interactions. Our observations suggest that there is a genetic locus for social cognition, which is imprinted and is not expressed from the maternally derived X chromosome. Neuropsychological and molecular investigations of eight females with partial deletions of the short arm of the X chromosome indicate that the putative imprinted locus escapes X-inactivation, and probably lies on Xq or close to the centromere on Xp. If expressed only from the X chromosome of paternal origin, the existence of this locus could explain why 46,XY males (whose single X chromosome is maternal) are more vulnerable to developmental disorders of language and social cognition, such as autism, than are 46,XX females.

Two hundred and eleven patients with a clinical diagnosis of Turner syndrome were studied. We report (i) the cytogenetic results, (ii) the frequency of cryptic mosaicism and (iii) the parental age and the parental origin of the abnormality. We scored 100 cells from blood cultures and found 97 patients to have a 45,X constitution, 15 to be 45,X/46,XX or 45,X/47,XXX mosaics, 86 to have a structurally abnormal X and 13 to have a structurally abnormal Y chromosome. Molecular methods were used to look for cryptic X and Y chromosome mosaicism in patients with a 45,X constitution. Two cryptic X but no cryptic Y mosaics were detected. In 74% of the 45,X patients the X was maternal in origin. The i(Xq)s were approximately equally likely to involve the paternal or maternal chromosome, while the majority of deletions and rings and virtually all the abnormal Y chromosomes were paternal in origin. We suggest that the preponderance of paternal errors in Turner syndrome may result from the absence of pairing along the greater part of the XY bivalent during paternal mei I, which may make the sex chromosomes particularly susceptible to both structural and non-disjunctional errors during male gametogenesis.

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