Ring Chromosome 20 (R20) is a rare condition, which causes epilepsy in children. It is caused by an abnormality in chromosome number 20. Chromosomes are structures within each cell in the body, which hold our genetic material. Each human being has 23 pairs of chromosomes - 46 in total.
When viewed down a microscope, chromosomes usually look 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 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 a mild learning disability before the start of epilepsy.
There is a variety of seizure types. Night time seizures are frequent and may not be noticed. Focal (partial) seizures can take on many forms including head turning, jerking of one or more limbs, and episodes of altered consciousness with repetitive mouth 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. It is associated with a change of behaviour, ranging from mild confusion to a severe altered state of consciousness. These episodes can last from 30 minutes to days or even weeks in some cases.
The start of epilepsy in R20 often comes before a decline in the person’s learning abilities and behaviour. Behaviour problems can be severe and deteriorate to the extent that many children are referred to specialist services before the diagnosis is made.
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 delayed. Brain scans are normal in children with R20.
Epilepsy Action has more information about diagnosing epilepsy
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 in isolation or in combination, may be tried. There are a small number of single case reports suggesting that vagus nerve stimulation may be effective in R20. Periods of NCSE are also difficult to treat. Short-term treatment with benzodiazepines (clobazam, midazolam, diazepam) or steroid medicines (prednisolone) may be used to treat these episodes,but the person often has further episodes of NCSE when these medicines are withdrawn.
Information about treatments for children can be found on the Medicines for Children website.
There may be research studies open that are relevant to this epilepsy syndrome. Your child’s doctor will be able to discuss this with you.
If your child has this syndrome they may have prolonged or repeated seizures. Your child’s doctor will discuss a ‘rescue’ or emergency care plan with you to treat any prolonged or repeated seizures.
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 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, and Dr Rachel Kneen, consultant paediatric neurologists at Alder Hey Children’s Hospital, Liverpool, UK and
• Dr Stewart Macleod, consultant paediatric neurologist at Royal Hospital for Sick Children, Glasgow, UK.
They have kindly prepared the information on this page. It is based on their own research, experience and expertise.