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.

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.

No abstract

Two unrelated chromosome abnormalities were found in equine half sibs. The proposita, Case 1, which was short in stature and infertile, had a de novo unbalanced X;15 translocation involving loss of Xp. Replication studies indicated that the translocated X was preferentially late replicating and that this late replication spread variably into the autosomal segment. Case 2, a half brother of the proposita, was short in stature, had cryptorchidism, and was trisomic for chromosome 28. Cytogenetic analysis of the dam, the sire of Case 1, and two other phenotypically normal half sibs revealed normal chromosome complements. Five further normal pregnancies were reported. The finding of two unrelated chromosome abnormalities is therefore probably fortuitous in this family. This is the first case of an unbalanced X-autosome translocation and the first case of an autosome trisomy to be reported in the horse.