Turner syndrome: a cytogenetic and molecular study

TLDR

The study reports cytogenetic findings, the prevalence of cryptic mosaicism, and the parental age and origin of the chromosomal abnormalities in Turner syndrome. A cohort of 211 Turner syndrome patients was examined, and molecular techniques were applied to detect cryptic X and Y chromosome mosaicism in those with a 45,X karyotype. Among the patients, 97 had a 45,X constitution, 15 were mosaics, 86 had structurally abnormal X chromosomes, 13 had abnormal Y chromosomes, two cryptic X mosaics were found, 74 % of 45,X cases had a maternal X, and most structural abnormalities and abnormal Y chromosomes were paternal, suggesting paternal meiotic errors contribute to Turner syndrome.

Abstract

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.