Ring Chromosome 20 (R20) is a rare condition and one that often causes epilepsy in children. It is due to an abnormality in chromosome number 20. Chromosomes are very important structures within each cell in the body, which hold our genetic material. Each human being has 23 pairs of chromosomes - 46 in total.
When looked at down a microscope, chromosomes are usually fairly straight. In R20 a little piece of genetic material is missing from each end of one of the number 20 chromosomes, and the ends fuse or join together to form a ring. This happens very early in pregnancy. It happens sporadically (by chance) and therefore does not usually affect more than one child in the family.
The first symptom of R20 is usually epilepsy. This can start at any time from day one of life until 17 years. The person may have mild or moderate learning disabilities before the start of epilepsy.
There is a variety of seizure types. Most seizures are focal (previously called partial) and usually occur during the night. Because of this they may not be noticed at first. The focal seizures can take on many forms. These include head turning, stiffness, twisting or jerking of one or more limbs, and episodes of altered awareness with or without repetitive mouth or eye movements. Tonic-clonic and absence seizures can also happen. People with R20 seem particularly prone to episodes of non-convulsive status epilepticus (NCSE). This is when there is continuous abnormal electrical activity from the brain – which can be easily seen during an EEG. NCSE often appears as a change in behaviour, ranging from mild confusion, drooling and not speaking to a severe altered state of awareness. Brief twitching or jerks of the limbs or face may also occur during NCSE. Episodes of NCSE can last from 30 minutes to days or even weeks in some cases.
Epilepsy in R20 often starts before a decline in the person’s learning abilities and behaviour. Behaviour problems can be severe and get worse to the extent that many children will need to be referred to specialist services before the diagnosis is made. The behaviour problems can include poor concentration, being impulsive and having periods of irritability and screaming.
A diagnosis is made by examining the child’s chromosomes under a microscope. This involves a blood test.
Severe epilepsy with periods of NCSE associated with the start of learning and behaviour difficulties may suggest a diagnosis of R20. Some EEG features seem to be fairly common in R20, and may again suggest the diagnosis. Unfortunately, because the condition is so rare, the diagnosis is often not considered and therefore the diagnosis is delayed. Sometimes children are first thought have to Lennox-Gastaut or Landau-Kleffner syndrome but finding the abnormal chromosome confirms the diagnosis of R20. Brain scans are normal in children with R20.
Some children that have an abnormality of their chromosomes may look a little different than other children of their age. However, most children with R20 look no different than any other children of their age.
The epilepsy associated with R20 syndrome is difficult to control. No single epilepsy medicine has been shown to be particularly effective, and many medicines, either singly or in combination, may be tried. There are a small number of single case reports suggesting that vagus nerve stimulation (VNS) may be effective in R20. Periods of NCSE are also difficult to treat. NCSE may respond to treatment with benzodiazepines (clobazam, midazolam, diazepam) or steroid medicines (prednisolone) given for a few days or up to a couple of weeks. Unfortunately, NCSE may often come back after these medicines are withdrawn.
Information about treatments for children can be found on the Medicines for Children website.
There may be research studies taking place that are relevant to this epilepsy syndrome. Your child’s hospital doctor will be able to discuss this with you.
If your child has this syndrome they may have prolonged or repeated seizures. They are also likely to have episodes of NCSE. Your child’s hospital doctor will discuss a ‘rescue’ or emergency care plan with you to treat any prolonged or repeated seizures or NCSE.
The long-term outlook for people with R20 is variable and depends on the person, the severity of the epilepsy and the associated learning and behavioural problems. More research studies are needed to clarify the longer-term outlook for people with R20.
What is a syndrome?
A syndrome is a group of signs and symptoms that, added together, suggest a particular medical condition. In epilepsy, examples of these signs and symptoms would be things like the age at which seizures begin, the type of seizures, whether the child is male or female and whether they have physical or learning disabilities, or both. The results of an electroencephalogram (EEG) are also used to help identify epilepsy syndromes.
If you would like to know more about an epilepsy syndrome, please speak to your doctor. If you would like to know more about epilepsy in general, please contact Epilepsy Action.
Epilepsy Action would like to thank Dr Richard Appleton, consultant paediatric neurologist at Alder Hey Children’s Hospital, Liverpool, UK for preparing this information.