Characterization of a rare mosaic X-ring chromosome in a patient with Turner syndrome

BACKGROUND: Ring chromosomes can be formed by terminal breaks of two arms of a chromosome and their rejoining, leading to a loss of genetic material. They may also be formed by telomere-telomere fusions with no deletion, resulting in the formation of a complete ring. Mosaic X-ring chromosomes are extremely rare and have highly variable phenotypes. Here, we report a case with a mosaic X-ring chromosome in a patient with Turner syndrome, and we illustrate the unreported complicated mechanism using chromosome analysis and fluorescence in situ hybridization (FISH). CASE PRESENTATION: A 10-year-old girl of short stature presenting Turner syndrome was admitted to our hospital. The patient’s clinical characteristics were subsequently documented. Genetic analysis showed a karyotype of mostly 45,X[140]/46,X,r(X)[60]. The X ring chromosome was cytogenetically characterized as 45,X/46,X,r(X)(p22.32q21.1), with a length of approximately 74 Mb. CONCLUSIONS: Taken together, we report a rare case with a mosaic X ring chromosome in Turner syndrome and we believe this case expands our collective knowledge of mosaic structural chromosomal disorders and provides new insight into clinical management and genetic counseling for Turner syndrome.