Triple Mosaic Turner Syndrome: An Exceptionally Rare Cytogenetic Variant

Background: Turner syndrome (TS) demonstrates substantial clinical, phenotypic, and cytogenetic heterogeneity, particularly in mosaic forms that often create diagnostic and prognostic challenges. Triple mosaic variants involving the X chromosome are exceedingly rare and remain poorly characterized, limiting the understanding of their clinical significance and genotype-phenotype correlations. Reporting such a rare mosaic pattern contributes to expanding the cytogenetic spectrum of TS and aids in the clinical interpretation of complex mosaic outcomes associated with primary amenorrhea (PA). Case Presentation: A comprehensive clinical, endocrinological, cytogenetic, and molecular cytogenetic evaluation was carried out on a 17-year-old female presenting with PA. Peripheral blood lymphocyte chromosomes were analyzed using conventional G-banded karyotyping and fluorescence in situ hybridization (FISH) with the DXZ1 centromeric probe, following the AGT Cytogenetics Laboratory Manual (4th edition). A conventional karyotype revealed a rare triple mosaic karyotype pattern of mos 45,X[30]/46,X,i(X)(q10)[7]/46,XX[3], consistent with TS. FISH confirmed the presence of X chromosome mosaicism by demonstrating nuclei with one and two X-centromeric signals; however, it did not differentiate between the 46,XX and 46,X,i(X)(q10) cell populations. Conclusion: The current case highlights the diagnostic significance of the rare triple mosaic TS karyotype in the evaluation of PA. Although the predominance of the 45,X cell population may have influenced the phenotype, genotype-phenotype correlations should be interpreted cautiously because mosaicism was assessed only in peripheral blood lymphocytes. This rare cytogenetic finding presents diagnostic challenges that require integrated conventional G-banded karyotyping and complementary FISH for accurate cytogenetic characterization.