r(20) syndrome is a very rare condition in which one of the two copies of chromosome 20 has formed a ring rather than the typical linear chromosome structure. Why the tips of the chromosome join together to form the ring is not understood and how the formation of the ring affects the function of genes packaged on chromosome 20 is also not understood. The consequence of the ring formation is a difficult to control epilepsy, typically with onset in early childhood and associated with intellectual disability and behaviour problems which may be progressive. Sometimes the behavioural problems may present before the epilepsy. Seizures do not typically respond to treatment and there is currently no recommended treatment for r(20) syndrome.

We don’t know how common r(20) syndrome is, though it is perceived to be underdiagnosed or misdiagnosed in some people with epilepsy.

There are two distinct forms of r(20) syndrome: non-mosaic where the ring is found in every cell in the body (the most severe form of the disease) and mosaic, where the ring is seen in only a percentage of the cells (this is the more common form of the disease).