Ring chromosome 20

Alternate names

Chromosome 20 ring; Ring 20; R20; Ring chromosome 20 syndrome

Summary

• Ring chromosome 20 syndrome is one of the more common ring chromosome-associated conditions. This occurs when both ends of chromosome 20 are deleted and the ends join together to form a ring. The most obvious feature of this condition is epilepsy.
• Epilepsy usually manifests in infancy or early childhood, and usually does not respond well to medication.
• Some people with ring 20 chromosome have intellectual disability. A minority of those affected have abnormal facial features, low muscle tone, behavioral problems, or short stature.

Cause

• Ring chromosome 20 is caused by an abnormal chromosome 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.

Inheritance

• Ring chromosome 20 is usually not inherited.
• It almost always occurs by chance during the formation of reproductive cells (eggs or sperm) or in early embryonic development.

Signs and symptoms

• People with ring chromosome 20 often have recurrent seizures or epilepsy.
• Other symptoms might include intellectual disability, behavioral difficulties, growth delay, short stature, a small head (microcephaly), and characteristic facial features.

Diagnosis

Chromosome disorders may be suspected in people who have developmental delays, intellectual disabilities and/or physical abnormalities.

Several types of genetic tests can identify chromosome disorders:

• Karyotyping
• Microarray (also called array CGH)
• Fluorescence in situ hybridization (FISH)

Treatment

• Treatment of ring chromosome 20 is typically focused on management of seizures.
• The seizures associated with ring chromosome 20 do not generally respond well to medications.
• The treatment that is successful varies from person to person.
• ‘Broad spectrum’ anti-epileptic drugs are usually tried first since they are active against different seizure types.
• Examples include valproate, levetiracetam, lamotrigine, topiramate and zonisamide.
• Success has been reported in some people with a combination of valproate and lamotrigine, but so far no single therapy has worked for everyone.
• Vagus nerve stimulation (VNS) has been tried and a reduction in seizures has been reported in some cases but not in others.
• This involves implanting a medical device under the skin, similar to a pacemaker that delivers a mild electrical current to the brain via the vagus nerve. The long-term effectiveness of VNS therapy is not yet known.

External links

Classification
External resources	Orphanet: 1444