Complex mosaic form of trisomy chromosome 18 and monosomy chromosome X in a girl with esophageal atresia and mild developmental delay: Diagnostic and therapeutic challenge and a review of literature.

The coexistence of mosaic trisomy 18 and Turner syndrome represents an extremely rare genetic constellation, with only a few cases reported in the literature to date. We present the case of a 7-year-old girl with esophageal atresia, full trisomy 18 in lymphocytes, and mosaic copy number changes involving trisomy 18 with coexisting monosomy X in fibroblasts, suggesting the presence of additional cell populations lacking trisomy 18. In addition, we provide a review of the relevant literature. This case is of particular clinical significance, as it describes long-term survival in a child with Edwards syndrome and illustrates the diagnostic challenges associated with tissue-limited mosaicism. Furthermore, it underscores that an established diagnosis of one genetic disorder does not preclude the coexistence of another, particularly when the clinical phenotype deviates from the classical presentation of the primary syndrome. Adequate analysis of a sufficient number of metaphases in karyotyping is essential to reliably detect or exclude mosaicism in Edwards syndrome, as the distinction between full and mosaic trisomy 18 carries important prognostic implications.