A girl with an end-to-end fusion of two X'S

Turner syndrome mosaicism: an unusual case with a de novo large dicentric marker chromosome: mos 45,X/46,X, ter rea(X;X)(p22.3;p22.3)

X/X translocations are quite rare in humans. The effect of this anomaly on the phenotype is variable and depends on the amount of deleted material and whether the chromosomes are joined by their long or short arms. We report an unusual case of Turner syndrome mosaicism in a 16-year-old girl, who was referred to our Institute for primary amenorrhoea associated with short stature. Endocrine evaluation revealed hypergonadotropic hypogonadism, which required a study of the karyotype. Cytogenetic analysis, performed on peripheral blood leucocytes, showed a mos 45,X/46,X,ter rea (X;X)(p22.3;p22.3) de novo karyotype. The prevalent cell line was 45,X (90% cells). A second cell line (10% cells) showed a very large marker chromosome, similar to a large metacentric chromosome. FISH (fluorescent in situ hybridisation) and molecular analysis revealed that the marker chromosome was dicentric and totally derived from the paternal X chromosome.

Dicentric Y chromosome arising via tandem translocation

We describe a 22-year-old woman with primary amenorrhea, bilateral gonadoblastomas, and short stature (148.0 cm), but no other signs of the Ullrich-Turner syndrome. There were three cell lines identified in peripheral blood lymphocytes - 45,X (30%), 46,XY (60%), and 46,X,tan dic(Y) (10%). Cells cultured from gonadal biopsies showed only the 45,X karyotype. However, frozen sections of the biopsies showed frequent single and rare double-Y-chromatin bodies. Lymphocytes were H-Y antigen-negative. This previously undescribed structurally abnormal chromosome probably consists of two Y chromosomes attached end-to-end in a tandem translocation. One of the centromeres forms the primary (functional) constriction, the other being detectable only as C-positive material on each chromatid, so presumably inactive. The discrepancy between the presence of Y-chromatin in frozen sections of the gonads and its absence from karyotype in gonadal cultures is indicative of cell selection in tissue culture. Finally, the case confirms the high risk of gonadoblastoma in women with a Y chromosome, even in the absence of H-Y antigen.