Chromosome 20 ring syndrome. Ring chromosome 20. R20.
Incidence
Very rare syndrome. Sporadic.
Clinical Characteristics
A rare chromosomal anomaly in which both ends of chromosome 20 have been lost (deletion) and the two broken ends have reunited to form a ring-shaped figure. Seizures, behavior problems, variable degrees of mental retardation and minor anomalies are the most common clinical characteristics but there does not appear to be a constant pattern of dysmorphic signs. The first symptom of R20 is usually epilepsy and can start at any time from day one of life until 17 years. It is considered an epileptic syndrome. Patients may have mild learning difficulties before the start of epilepsy. There are a variety of seizure types. Nocturnal (night time) seizures are frequent and may not be noticed. Complex partial seizures can take on many forms including head turning, jerking of one or more limb 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). When this happens, there is continuous abnormal electrical activity from the brain (EEG) associated with a change of behaviour, ranging from mild confusion to a severe altered state of consciousness. These 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 may be severe and can deteriorate to the extent that many children are referred to a child psychiatric service before the diagnosis is made.
Precipitants
None
Provocation Tests
None
Diagnostic Procedures
Karyotype. Ring chromosome 20.