Ring Chromosome 12

The ring chromosome 12 (RC12) is an ultra-rare chromosomal disorder with only ten patients reported in the literature. Patients with RC12 often exhibit the typical features of “ring syndrome,” but also show distinct characteristics. These individuals are typically characterized by severe prenatal and postnatal growth failure, delayed development, intellectual disability, microcephaly, and distinct facial dysmorphism. Café-au-lait spots, clinodactyly, skeletal anomalies, and reproductive system abnormalities are also commonly observed in RC12 patients. All known cases of RC12 have occurred de novo. The unique and variable phenotypes observed in RC12 patients are likely due to the dynamic mosaicism caused by ring instability and the cytogenomic aberrations in the ring formation.