Ring chromosome 20, ring-shaped chromosome 20 or r(20) syndrome is a rare human chromosome abnormality where the two arms of chromosome 20 fuse to form a ring chromosome. The syndrome is associated with epileptic seizures, behaviour disorders and intellectual disability.When not all cells contain a ring chromosome 20, the individual has ring 20 chromosomal mosaicism. Ring Chromosome 20 syndrome is thought to be an underdiagnosed condition. Since chromosomal analysis or karyotype testing is not a routine investigation for patients with epilepsy, the diagnosis of ring chromosome 20 syndrome is typically delayed or unrecognized. Presentation
Recurrent seizures are the most recognizable feature of this syndrome and are most often the first sign of this syndrome. These syndromes are often ongoing and poorly responsive to anti-seizure medications. Most patients develop seizures the first few years of life, but the age of onset ranges from ages 1 to 17. Different types of seizure have been reported in this syndrome. The most common seizure type appears to be brief focal onset epileptic seizures with impairment of consciousness and awareness, known as complex partial seizures. Other features you may see in these complex partial seizures include staring, oral automatisms, unspecified automatic behavior, involuntary motor movements and/or head turning. Furthermore, many patients have subtle nighttime behavioral changes, such as stretching, rubbing, and turning resembling a nighttime awakening. However, electroencephalography (EEG) studies during these events show abnormal electrical seizure activity, indicating that nocturnal behavioral events are actually subtle nocturnal seizures or non-convulsive status epilepticus.
Optimal control of seizures appears to be the determining factor, but early diagnosis and a comprehensive management plan with multidisciplinary support is also thought be to be important. Research
Two international research studies are currently underway. The International Genetic Study done with the Spinner Laboratory at The Childrens Hospital of Philadelphia studies the ring 20 chromosome at the molecular level. The Clinical Research Study collects clinical information from parents to create a database of about the full spectrum of patients with ring chromosome 20 syndrome. References
Further reading
Schinzel A, Niedrist D (2001). "Chromosome imbalances associated with epilepsy". Am. J. Med. Genet. 106 (2): 119–24. doi:10.1002/ajmg.1576. PMID 11579431. External links
Ring Chromosome 20 Syndrome Map