Ring Chromosome 5

Human ring chromosome 5 (RC5) is rare, only accounts for approximately 1.3% of the reported human ring chromosomes (RCs). Cri-du-Chat syndrome and ring syndrome-associated phenotypes are the most common clinical findings in individuals with RC5 when the ring replaces a normal chromosome 5. Small supernumerary ring chromosome 5 (sSRC5) may result in different phenotypes. In addition, RC5-derived mosaicism is common due to ring instability. RC5 can be correctly identified by chromosome karyotyping and further analyzed by fluorescence in situ hybridization (FISH) using targeted locus-specific and chromosome painting probes on interphases and metaphases. The severity of the phenotypes resulting from a RC5 appears to be associated with the size and content of the deletion or duplication caused by the RC5. Therefore, detailed characterization using advanced genomic technologies to define breakpoints, genomic imbalance, and gene content in the RC5 for appropriate clinical assessment of affected individuals is recommended. Most patients of RC5 were de novo and postnatally diagnosed. However, inherited and prenatally diagnosed RC5 cases have been reported. Thus, parental studies and genetic counseling for newly diagnosed prenatal and postnatal RC5s are warranted.