Ring Chromosome 2

Ring chromosome 2 (RC2) in the context of a karyotype with a modal number of 46 chromosomes is an infrequently documented chromosomal structural abnormality. However, fourteen unique RC2 cases are reviewed here as the sole aberration. Males and females are equally represented, with one prenatal-only ascertainment. Notably, one individual had a natural history of up to 34 years. No normal cells were identified in at least seven individuals who displayed the monocentric ring as an isolated event with variable ring structures observed in a subset of cells. At least eleven individuals were de novo for RC2. Recurring break points at cytobands 2p25 and 2q37 are noted in the reported cases. Excessive cell death and genetic imbalance resulting in growth deficiency might depend on the degree of aneuploidy or mosaicism. Overall, mitotic instability of the ring is observed. An associated ring syndrome phenotype may be appreciated, which appears to differ from the features observed in individuals affected by pure terminal copy number changes. Cytogenomic follow-up testing is needed to improve accurate genotype–phenotype correlations. Beyond these initial reports, there is a paucity of longitudinal studies.