Cytomolecular Analysis of a Ring X Chromosome in a Patient with Turner Syndrome: A Case Report.

Introduction: Turner syndrome (TS) is a genetic disorder caused by the complete or partial absence of one of the X chromosomes. Its clinical features include short stature, gonadal dysgenesis, primary amenorrhea, and infertility. The condition presents significant phenotypic variability, especially in cases involving chromosomal mosaicism and structural abnormalities. Case Presentation: A 21-year-old female patient from Tapauá, Amazonas, Brazil, was evaluated due to irregular bleeding followed by secondary amenorrhea. Cytogenetic analysis of peripheral blood lymphocytes was performed using conventional G-banding, followed by fluorescence in situ hybridization (FISH) for molecular characterization. Cytogenetic analysis revealed two cell lines: one with monosomy X (45,X) and another with 46 chromosomes including a ring X chromosome. The final karyotype was mos45,X[170]/46,X,r(X)(p11.22q13.23)[30]. The presence of a ring X chromosome was confirmed by FISH. Conclusion: This case illustrates the relevance of combining classical and molecular cytogenetic techniques to identify structural X chromosome abnormalities. Such analysis is essential for accurate diagnosis, understanding genotype–phenotype correlations, and guiding clinical management and genetic counseling in patients with TS.