What is a ring chromosome?
A ring chromosome typically occurs when a chromosome breaks in two places and the ends of the chromosome arms fuse together to form a circular structure. In rare cases, ring formation occurs when there is only one break or no breaks. A ring chromosome can be derived from any chromosome number. Ring chromosomes typically result in mental and/or physical abnormalities. This is most likely due to the loss of genetic material in the ends of the chromosome when a ring forms. Some examples of disorders caused by ring chromosomes include: • ring chromosome 20 syndrome – associated with epilepsy • ring chromosome 14 syndrome – associated with mental retardation, skin pigment abnormalities, seizures and abnormal facial features • ring chromosome 13 syndrome – associated with mental retardation and abnormal facial features • ring chromosome 15 syndrome – associated with mental retardation, dwarfism and small head size (called microcephaly) • Ring formation of an X-chromosome results in Turner sy
