Ring chromosome 20 syndrome

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 mental retardation.

When only one copy of chromosome 20 forms a ring, the individual suffers from ring 20 chromosomal mosaicism.