TURNER-SYNDROME - A CYTOGENETIC AND MOLECULAR STUDY

Two hundred and eleven patients with a clinical diagnosis of Turner sy ndrome were studied. We report (i) the cytogenetic results, (ii) the f requency of cryptic mosaicism and (iii) the parental age and the paren tal origin of the abnormality. WE: scored 100 cells from blood culture s 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 dete cted. 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 mate rnal chromosome, while the majority of deletions and rings and virtual ly all the abnormal Y chromosomes were paternal in origin. We suggest that the preponderance of paternal errors in Turner syndrome may resul t from the absence of pairing along the greater part of the XY bivalen t during paternal mel I, which may make the sex chromosomes particular ly susceptible to both structural and nondisjunctional errors during m ale gametogenesis.