Dynamic Mosaicism Involving a Ring Chromosome 2 in a 4-Year-Old Male: Case Report and Literature Review

Ring chromosomes (RCs) are rare structural chromosomal abnormalities caused by terminal breaks and fusion of chromosome ends, occurring in approximately 1 in 50,000 live births. They are often associated with “ring chromosome syndrome,” characterized by growth restriction, mild dysmorphism, and variable intellectual disability, even without large deletions. Ring chromosome 2 is exceptionally rare, with fewer than 20 reported cases and limited molecular characterization. We report a 4-year-old male with proportional growth restriction, mild facial dysmorphism, and delayed expressive speech. Cytogenetic analysis identified a mosaic ring chromosome 2, and fluorescence in situ hybridization demonstrated preserved subtelomeric regions. However, array comparative genomic hybridization revealed a 46 kb deletion at 2p25.3 involving the protein-coding gene FAM110C. This case broadens the phenotypic and molecular spectrum of ring chromosome 2 and underscores the value of combining cytogenetic and high-resolution genomic techniques to detect cryptic imbalances contributing to clinical presentation.