Ring chromosome 22
Ring chromosome 22, also known as ring 22, is a rare chromosomal disorder. Ring chromosomes occur when the ends of a chromosome lose material and fuse into a ring shape; in the case of ring 22, this occurs for chromosome 22, the last numbered human autosome. Ring chromosome 22 is marked by a number of consistent traits, such as intellectual disability, speech delay, hypotonia, and hyperactivity. The condition has a similar phenotype to Phelan-McDermid syndrome, as the loss of the SHANK3 gene is implicated in both. Presentation Though ring chromosome 22 has a variable phenotype, a number of consistent features between most cases have been noticed. Most cases have intellectual disability, generally in the moderate to profound range. Other prevalent features include hypotonia (unusual weakness or floppiness of the skeletal muscles), significant hyperactivity, and autism-like features. Significant speech delay is common; in a sample of 35 cases with a median age of 10, over half of the participants were unable to speak, and those who did spoke their first words on average at nearly three years of age. Poor coordination and an unsteady gait are also frequent findings. A number of craniofacial anomalies are common, such as microcephaly, epicanthic folds,