Chromosome Ring 20 Syndrome

General Medical Guideline
Last modified
4 August 2020

Refractory epilepsy, with seizures in wakefulness and sleep, behavioural problems and mild to severe cognitive impairment are the main medical issues for people with a (mosaic) ring 20 chromosome.

In contrast to most chromosomal abnormalities, features as congenital malformations and facial dysmorphic characteristics, are rarely reported in r(20). Therefore, on the clinical findings alone it is difficult to diagnose the syndrome.

The diagnosis requires cytogenetic testing in children with refractory epilepsy and or behavioral problems. In the majority of reported cases the ring is present in only a proportion of cells, with two normal 20's in the remaining cells (mosaicism). Therefore the cytogeneticist should be aware of a possible mosaic and analyze more karyotypes (maybe up to 100) to look for an r(20). In the mosaic r(20) cases there seems to be no deletions of chromosome 20.

In some patients, the r(20) is found in all cells analyzed and in these cases, than the ring is almost always accompanied by deletions of 20pter and/or 20qter.


Elens et al (2012) find in a group of 6 persons with r(20), all presented with pharmaco-resistant frontal lobe complex partial seizures. Electroencephalogram recordings showed rhythmic theta waves with frontal predominance and non-convulsive status epilepticus (NCSE).

In a report by Vignoli et al (2016) the electro-clinical phenotype of 25 patients (aged 8-59 years) with r(20) are reviewed. ‘The epilepsy exhibited an age dependent course. When seizure onset occurred in childhood, terrifying hallucinations associated with focal motor seizures, often sleep-related, or dyscognitive seizures, were prominent features, often evolving into epileptic encephalopathy associated with non-convulsive status epilepticus. In the long-term, progressive stabilization of drug resistant epilepsy associated with non-convulsive status epilepticus, focal seizures with motor and autonomic features, and eyelid myoclonia were noticed. Epilepsy onset in adolescence was accompanied by a milder developmental course, dyscognitive seizures and non-convulsive status epilepticus, and no cognitive decline. Only three older patients became seizure free (>5 years).’ They found statistically significant correlations between age at epilepsy onset and cognitive level.

The treatment of epilepsy associated with r(20) syndrome is difficult. No single anti-epileptic medicine has been shown to be effective. Many medicines, either single or in combination with others, have been tried. 

Developmental disability

People with r(20) may have mild or moderate learning disabilities before the start of epilepsy.

On the other hand learning disabilities can be due to the epilepsy. NCSE appears as behavior change, like confusion, drooling and not speaking and even a severe altered state of awareness. Episodes of NCSE can last from 30 minutes to days or even weeks in some cases. The episodes of non-convulsive status epilepticus (NCSE), a continuous abnormal electrical activity from the brain, can be easily seen during an EEG. Source: Epilepsy UK

Seizures may be mistaken for attention deficit disorders. Innovative technical devices (like the Epihunter Pro) can built  automatically a seizure diary available through a webportal. The home-care solution is based on a wearable EEG headband and a smartphone with a detection algorithm. When a seizure is detected, the people around are notified immediately. The tool may help teachers and others to warn the individual has a seizure.

Rare Condition

Chromosome Ring 20 Syndrome

Chromosome Ring 20 syndrome is a rare chromosomal disorder characterized by medically hard to control epilepsy, nocturnal subtle seizures, behavioural problems and mild mental impairment...