Ring Chromosome 20 (R20) is a condition that comes from an abnormality in chromosome 20. R20 is a rare condition that can quite often be the cause of epilepsy in children. Each human being has 23 pairs of chromosomes (giving them 46 in total), these important structures are held within each cell of the body and hold our genetic material.
Chromosomes when inspected using a microscope should appear fairly straight, however, with R20 there is a tiny piece of genetic material missing from both ends of the number 20 chromosome. This causes the ends to fuse together and create a ring rather than a straight line.
This chromosome abnormality will happen very early during pregnancy and happens completely by chance, which means it’s not a genetic defect and it’s highly unlikely to happen to more than one child in the same family.
Epilepsy is actually a symptom of R20, and it’s often the first one. However, a child can present with epilepsy from day 1 right up until they are 17 years. In some cases, mild to moderate learning difficulties may be apparent before epilepsy.
Children with R20 and epilepsy can often have a variety of seizure types. Focal (partial) are the most common and these usually happen whilst sleeping. Head turning, stiffness and limb jerking are all common forms of a focal seizure. Tonic-clonic and absence seizures can also be fairly common with this particular syndrome.
Children with R20 also seem to be particularly susceptible to non-convulsive status epilepticus, a continuous abnormal electrical activity within the brain which can be seen during an Electroencephalography (EEG) test.
An examination of the child’s chromosomes under a microscope is the only way to make a diagnosis of R20.
The combination of epilepsy with learning or behaviour difficulties may be enough to suggest a diagnosis of R20 and lead to an analysis of the chromosomes. However, because the syndrome is so rare it’s often mistaken for Lennox-Gastaut or Landau-Kleffner syndrome.
Treatment for epilepsy with R20 has proved to be extremely difficult. There is no single epilepsy medication that has proved to be particularly effective at controlling seizures. For this reason, it can take some time to find the optimal anti-epileptic medication (AED) or a combination of AEDs to treat R20.
There are some reports that vagus nerve stimulation (VNS) can be an effective treatment option for children with R20.
The prognosis for children with R20 is very wide and varying. This can depend on the severity of the epilepsy and the learning and behavioural difficulties experienced. There is a need for much more research on R20 and the long term effects on those who have it.
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