Cytogenomic characterization of mosaic X-ring chromosomes in seventeen patients with Turner syndrome (TS)-42 years of experience at a single-site institution.

Individuals with Turner syndrome (TS) phenotypes may exhibit short stature, ovarian dysfunction, and neurocognitive disorders. Their genomes can include ring chromosomes formed from the X chromosome (RCX). Here, we present cytogenomic and clinical findings from seventeen individuals with TS who bore mosaic forms of RCX and frequently presented with short stature and concern for TS. The subjects were retrospectively included and tested at a single-site cytogenetics laboratory for over 42 years. Here, we illustrate each subject's comprehensive cytogenetic workup and phenotypes. The cohort shows comorbidities and sexual characteristics associated with mosaic RCX. These cytogenetic findings and clinical features are distinct from those of individuals with non-mosaic TS. Studying the pattern of X-activation across tissues in this cohort could provide additional data on a postulated source of phenotypic variability. Current guidelines recommend karyotype as the first-line test rather than SNP microarray analysis when aneuploidy is suspected. Conventional cytogenetics is still necessary to understand structural abnormalities, provide genomic context, and detect low-level mosaicism. These cases add to the knowledge of mosaic RCXs and offer new clinical laboratory information that is important for diagnosis and useful for comprehensively caring for and managing TS patients.