X/XY Chromosome Mosaicism: Turner Syndrome and Other Clinical Conditions

The 45,X/46,XY mosaicism shows a wide spectrum of phenotypes ranging from females with Turner syndrome, male or female pseudohermaphroditism, to appearently normal male development. Chromosome anomalies accompanying Turner syndrome were found in lymphocyte cultures of 236 patients. Chromosomal analysis revealed the karyotype 45,X in 118 (50.0%) patients. X monosomy mosaics or structural rearrangements of the X chromosome was established in 112 (47.5%) patients. The Y chromosome was found in six (2.5%) patients with typical features of Turner syndrome. In five mosaics 45,X/46,XY the proportion of the XY clone ranged from 46% to 76%. In one Turner syndrome patient only 47,XYY cells were found (solely blood culture investigated). In most cases of 45,X/46,XY mosaicism, the cause is considered to be the loss of the Y chromosome because of nondisjunction after normal disomic fertilisation. Five other patients with X/XY chromosome mosaicism showed mixed gonadal dysgenesis (two patients), one male pseudohermafroditism, one male with Pierre Robin syndrome, and one normal male phenotype. In two non Turner syndrome patients nondisjunction of the primary clone 46,XY was obvious and resulted in mosaicism 45,X/46,XY/47,XYY, the one patient contained dicentric Y. The similarities between X/XY Turner syndrome and other nosological entity of females possessing Y chromosome — the Swyer syndrome — are discussed.