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.