What is ring chromosome 20 syndrome?

Ring chromosome 20 syndrome (RC20) is one of a number of chromosomal disorders associated with difficult to control epilepsy.

  • A ring chromosome is formed by the fusion of two arms of a straight chromosome during pre-natal (before birth) development. Why the formation of the ring causes epilepsy and other symptoms of the syndrome is not well understood.
  • The problems associated with this syndrome can occur from birth to 17 years old.  
  • Development is usually normal before the onset of seizures.
  • Clinically this syndrome is characterized by frequent subtle seizures at night.
  • This syndrome is also characterized by behavioral problems, mild cognitive impairment and learning disabilities.

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  • Seizures usually are the first and major clinical symptom of this syndrome, and usually do not respond to medications. 
  • They are often complex partial, usually with altered consciousness, staring, oral automatisms, unspecified automatic behavior, focal motor symptoms and/or head turning.
  • Subtle nocturnal behavioral changes such as stretching, rubbing, turning that resemble arousal, subtle nocturnal seizures (SNS), and subtle nocturnal frontal lobe seizures (SNFL) have also been reported in studies of RC20 patients.
  • Diagnosing this type of epilepsy is most easily done by looking at the chromosome pattern (called performing a karyotype) in blood cells but any other tissue including skin could be examined.
  • Epilepsy is not present in all individuals with RC20, however, it is the most consistent clinical feature. Unlike other chromosomal disorders with epilepsy, malformed organs or appearance and other congenital malformations are rarely seen.
  • Children can be misdiagnosed with Lennox-Gastaut syndrome or Landau-Kleffner syndrome. These two epilepsy syndromes have clinical similarities to RC20 and are characterized by frequent seizures, decline in learning ability and behavior and often termed as cognitive epileptic encephalopathies.
  • RC20 syndrome phenotype can also be mistaken for autosomal dominant nocturnal frontal lobe epilepsy (ADNFE). ADNFE is a familial partial epilepsy causing frequent, violent, brief seizures at night. Seizures usually begin in childhood and are easily controlled with carbamazepine, unlike seizures in RC20 syndrome.
  • The EEG features in RC20 may also have overlapping features of continuous slow spike and wave discharges in slow wave sleep (CSWS) and electrical status epilepticus in sleep (ESES).
  • RC20 epilepsy is a rare condition, but its actual frequency is unknown. More than 60 cases have been reported in the medical literature. Since chromosomal analysis or karyotype testing is not a routine investigation when refractory epilepsy first presents, the diagnosis of RC20 may be delayed or go unrecognized. In other words, some people with difficult-to-control epilepsy may have a ring chromosome 20 but be unaware of it.

How is this syndrome diagnosed?

Ring Chromosome 20 syndrome is diagnosed by recognition of the features outlined above and through looking at the pattern of chromosomes in the person’s cells. 

How is this syndrome treated? 

Seizures with RC20 are typically difficult to treat but seizure control is very important. Every situation is different and complex. Antiepileptic drugs are the mainstay and first line of treatment, however no one drug or treatment has been shown to be better than others. Patients are frequently exposed to multiple antiepileptic drugs. Usually surgery is not helpful for people with RC20, because seizures are usually not localized to one area. Vagus nerve stimulation has been successful in a few cases reported in the literature.

For more help

Ring Chromosome 20 Foundation

After years of testing, misdiagnosis, and a difficult journey, the Ford family was told that their young daughter Cara was having frequent and severe seizures due to ring chromosome 20 syndrome. With so little information about the syndrome available, Cara’s father, Stewart Ford, decided to establish a Foundation to fund research and projects so that families and doctors can better understand this condition and its treatment.

The purpose of the Ring Chromosome 20 Foundation is to promote awareness of the syndrome and the importance of chromosomal testing in children with refractory epilepsy. The Foundation is based in New York City and in London. For more information about this syndrome and the Foundation, please visit www.ring-chromosome-20.org

 

Authored by: Dr. Syed Hosain | Robert S. Fisher, MD, PhD on 9/2013
Reviewed by: Robert S. Fisher, MD, PhD on 9/2013
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