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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®

Ring chromosome 20 syndrome

Reviewed May 2009

What is ring chromosome 20 syndrome?

Ring chromosome 20 syndrome is a condition that affects the normal development and function of the brain. The most common feature of this condition is recurrent seizures (epilepsy) in childhood. The seizures may occur during the day or at night during sleep. They are described as partial seizures because they affect only one area of the brain, a region called the frontal lobe. In many cases, the seizures are complex and resistant to treatment with anti-epileptic drugs. Prolonged seizure episodes known as non-convulsive status epilepticus also appear to be characteristic of ring chromosome 20 syndrome. These episodes involve confusion and behavioral changes.

Most people with ring chromosome 20 syndrome also have some degree of intellectual disability and behavioral difficulties. Although these problems can appear either before or after the onset of epilepsy, they tend to worsen after seizures develop. Additional features of this condition can include slow growth and short stature, a small head (microcephaly), and subtle differences in facial features. Major birth defects are rarely seen with ring chromosome 20 syndrome.

How common is ring chromosome 20 syndrome?

Ring chromosome 20 syndrome appears to be a rare condition, although its prevalence is unknown. More than 60 affected individuals have been reported in the medical literature.

What are the genetic changes related to ring chromosome 20 syndrome?

Ring chromosome 20 syndrome is caused by a chromosomal abnormality known as a ring chromosome 20 or r(20). A ring chromosome is a circular structure that occurs when a chromosome breaks in two places and its broken ends fuse together. People with ring chromosome 20 syndrome have one copy of this abnormal chromosome in some or all of their cells.

It is not well understood how the ring chromosome causes the signs and symptoms of this syndrome. In some affected individuals, genes near the ends of chromosome 20 are deleted when the ring chromosome forms. Researchers suspect that the loss of these genes may be responsible for epilepsy and other health problems. However, other affected individuals do not have gene deletions associated with the ring chromosome. In these people, the ring chromosome may change the activity of certain genes on chromosome 20, or it may be unable to copy (replicate) itself normally during cell division. Researchers are still working to determine the precise relationship between the ring chromosome 20 and the characteristic features of the syndrome.

Related Chromosome(s)

Changes involving this chromosome are associated with ring chromosome 20 syndrome.

  • chromosome 20

Can ring chromosome 20 syndrome be inherited?

Ring chromosome 20 syndrome is almost never inherited. A ring chromosome typically occurs as a random event during the formation of reproductive cells (eggs or sperm) or in early embryonic development. Often, the ring chromosome is present in only some of a person's cells. This situation is known as mosaicism.

Most affected individuals have no history of the disorder in their families. However, at least one family has been reported in which a ring chromosome 20 was passed from a mother to her children.

Where can I find information about diagnosis or management of ring chromosome 20 syndrome?

These resources address the diagnosis or management of ring chromosome 20 syndrome and may include treatment providers.

  • Genetic Testing Registry: Ring chromosome 20 syndrome (
  • MedlinePlus Encyclopedia: Chromosome (
  • MedlinePlus Encyclopedia: Epilepsy (

You might also find information on the diagnosis or management of ring chromosome 20 syndrome in Educational resources and Patient support.

General information about the diagnosis ( and management ( of genetic conditions is available in the Handbook. Read more about genetic testing (, particularly the difference between clinical tests and research tests (

To locate a healthcare provider, see How can I find a genetics professional in my area? ( in the Handbook.

Where can I find additional information about ring chromosome 20 syndrome?

You may find the following resources about ring chromosome 20 syndrome helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for ring chromosome 20 syndrome?

  • r(20) syndrome
  • ring 20 syndrome
  • ring chromosome 20
  • ring chromosome 20 epilepsy syndrome

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines ( and How are genetic conditions and genes named? ( in the Handbook.

What if I still have specific questions about ring chromosome 20 syndrome?

Ask the Genetic and Rare Diseases Information Center (

What glossary definitions help with understanding ring chromosome 20 syndrome?

cell ; cell division ; chromosome ; disability ; embryonic ; epilepsy ; epileptic ; gene ; inherited ; microcephaly ; mosaicism ; prevalence ; reproductive cells ; seizure ; short stature ; sperm ; stature ; status epilepticus ; syndrome

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Alpman A, Serdaroglu G, Cogulu O, Tekgul H, Gokben S, Ozkinay F. Ring chromosome 20 syndrome with intractable epilepsy. Dev Med Child Neurol. 2005 May;47(5):343-6. (
  • Augustijn PB, Parra J, Wouters CH, Joosten P, Lindhout D, van Emde Boas W. Ring chromosome 20 epilepsy syndrome in children: electroclinical features. Neurology. 2001 Sep 25;57(6):1108-11. (
  • Canevini MP, Sgro V, Zuffardi O, Canger R, Carrozzo R, Rossi E, Ledbetter D, Minicucci F, Vignoli A, Piazzini A, Guidolin L, Saltarelli A, dalla Bernardina B. Chromosome 20 ring: a chromosomal disorder associated with a particular electroclinical pattern. Epilepsia. 1998 Sep;39(9):942-51. (
  • de Falco FA, Olivieri P, de Falco A, Concolino D, Battaglia F, Verardi R, Grande G, Stabile M. Electroclinical evolution in ring chromosome 20 epilepsy syndrome: a case with severe phenotypic features followed for 25 years. Seizure. 2006 Sep;15(6):449-53. Epub 2006 Jun 27. (
  • Inoue Y, Fujiwara T, Matsuda K, Kubota H, Tanaka M, Yagi K, Yamamori K, Takahashi Y. Ring chromosome 20 and nonconvulsive status epilepticus. A new epileptic syndrome. Brain. 1997 Jun;120 ( Pt 6):939-53. Review. (
  • Nishiwaki T, Hirano M, Kumazawa M, Ueno S. Mosaicism and phenotype in ring chromosome 20 syndrome. Acta Neurol Scand. 2005 Mar;111(3):205-8. (
  • Unique support group booklet about ring chromosome 20 (
  • Ville D, Kaminska A, Bahi-Buisson N, Biraben A, Plouin P, Telvi L, Dulac O, Chiron C. Early pattern of epilepsy in the ring chromosome 20 syndrome. Epilepsia. 2006 Mar;47(3):543-9. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: May 2009
Published: February 8, 2016