Ring Chromosome 21

Ring chromosome 21 (RC21) is detected using karyotyping, fluorescence in situ hybridization (FISH), and chromosome microarray analysis (CMA) to define its ring structure, dynamic mosaicism, and genomic imbalances. Patients with RC21 show a broad spectrum of phenotypes from apparently normal to obvious intellectual disability, developmental delay, microcephaly, craniofacial dysmorphisms, epilepsy, hearing and vision problems, and congenital anomalies in central nervous, cardiovascular, musculoskeletal systems. Thrombocytopenia and acute leukemias can occur in newborn to adult and could be treated effectively to achieve complete remission. Reproductive disorders of azoospermia and infertility are noted in most adult male patients, and increased risk of miscarriages and fetuses with rearranged chromosome 21 are noted in adult female patients. Around 70% of the RC21 cases are found to be de novo while 30% are familial, mostly due to maternal transmissions. Integrated cytogenomic analysis should be performed for patients with RC21; follow-up parental study and chromosome analysis on bone marrow cells in the cases with acute leukemias are recommended. Examination of growth and psychomotor skills, multiple congenital anomalies, and evaluation of infertility are recommended. Furthermore, clinical management for individuals with RC21 should include treatment of congenital anomalies, epilepsy, and acute leukemias.