Clinical spectrum and Cytogenetic characterization of patients with Turner Syndrome – Twin case report

Diagnosis of Turner syndrome (TS) is usually made in mid-childhood, where 50% of the patients have 45, X karyotype in peripheral lymphocytes, which results from haploinsufficiency of the genes that commonly escape X-inactivation. 30%–40% have mosaicism of different forms, like 45,X/46,X,dic(Xp)/46,X,idic(Xq) and less commonly 45,X/46,XY. The goal of this case report is to analyze the cytogenetic and molecular characterization of two cases with dicentric X chromosomal abnormalities with varying degrees of mosaicism, demonstrating shared clinical features of TS. Combined conventional cytogenetic analysis, centromere banding, and fluorescence in situ hybridization (FISH) was done for the patients who presented with short stature and irregular menstrual cycles. Chromosome studies showed two cell lines: one with a single copy of X chromosome (45,X) and the other with a structural variation in X chromosome (isodicentric X chromosome), which is described as a Turner variant. C-banding also revealed the presence of two centromeres. Metaphase FISH with centromere probes for X revealed two mosaic cell lines: one with 45,X and a second one showing isodicentric X chromosome. The accurate diagnosis and characterization of a genomic imbalance in patients with sex chromosome disorders are essential for evaluating phenotype–karyotype correlations, genetic counseling, and having a clinical follow-up.