Ring Chromosome 9

Ring chromosome 9 (RC9) is a rare structural chromosome abnormality. Karyotyping, fluorescence in situ hybridization (FISH), chromosome microarray analysis (CMA), and genomic sequencing have been used to define the ring structure, dynamic mosaicism, genomic imbalances, and ring formation mechanism from cases of RC9. All reported cases of RC9 showed an incomplete and instable ring and occurred de novo by follow-up parental studies. Prenatal diagnosis and genetic counseling are effective for parents to make informative decision on the termination of pregnancies. Postnatally, general ring syndrome features of severe growth retardation, microcephaly, mild to moderate intellectual disability were noted in most patients with RC9. Neonatal and childhood death can occur because of cardiac arrest and pneumonia. Azoospermia is expected in adult male patients with RC9. Patients should be evaluated for congenital heart defects, respiratory complications, genital anomalies, and seizures based on the gene content in the genomic imbalances of the RC9.