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Human genetic disorders can be caused by ring chromosome formation. Although ring chromosomes are very rare, they have been found in all human chromosomes. Symptoms seen in patients carrying ring chromosomes are more likely to be caused by the deletion of genes in the telomeric regions of affected chromosomes, rather than by the formation of a ring structure itself. [5]
In some cases, the signs and symptoms are similar to those of Down syndrome. Changes to chromosome 21 include a missing segment of the chromosome in each cell (partial monosomy 21) and a circular structure called ring chromosome 21. A ring chromosome occurs when both ends of a broken chromosome are reunited.
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 14 syndrome is a very rare human chromosome abnormality. It occurs when one or both of the telomeres that mark the ends of chromosome 14 are lost, allowing the now uncapped ends to fuse together – thus forming a ring chromosome. It causes a number of serious health issues. [1] [3] [4]
In humans, when a Robertsonian translocation joins the long arm of chromosome 21 with the long arm of chromosomes 14 or 15, the heterozygous carrier is phenotypically normal because there are two copies of all major chromosome arms and hence two copies of all essential genes. [9]
The ring is formed when the caps on both the long arm (q) and the short arm (p) of one copy of chromosome 18 are lost and the new ends re-join to form the ring. Because the ring involves deletions of both the long arm (18q-) and the short arm (18p-) of chromosome 18, individuals with ring 18 can have features of both 18p- as well as distal 18q- .
Ring chromosome 20, ring-shaped chromosome 20 or r(20) syndrome is a rare human chromosome abnormality where the two arms of chromosome 20 fuse to form a ring chromosome. The syndrome is associated with epileptic seizures , behaviour disorders and intellectual disability.
22q11.2 distal deletion syndrome is a rare genetic condition caused by a tiny missing part of one of the body's 46 chromosomes – chromosome 22. 22q11.2 distal deletion syndrome appears to be a recurrent genomic disorder distinct from 22q11.2 deletion syndrome also known as DiGeorge syndrome (DGS; 188400) and velocardiofacial syndrome (VCFS; 192430).