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 Presentation · Genetics · Treatment. Methods To understand the structure and composition of the ring chromosome 20 (r(20)) in this patient cohort, blood specimens from 28 affected individuals. Ring chromosome 20 syndrome is a condition that affects the normal development and function of the brain. The most common feature of this condition is.
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Ring chromosome 20 syndrome - Wikipedia
Presentation[ edit ] 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 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.
Furthermore, many patients have subtle nighttime behavioral changes, such as stretching, rubbing, and ring chromosome 20 resembling a nighttime awakening.
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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.
Many of these patients experience their seizures only during sleep. Ring chromosome 20 can have seemingly bizarre features as they originate from the frontal lobe of the brain.
Often, individuals with ring chromosome 20 syndrome are initially found to have complex partial seizures of frontal lobe origin, though imaging studies do ring chromosome 20 show a corresponding structural brain abnormality. In certain patients, these seizures may secondarily generalized.
Ring chromosome 20 syndrome
Individuals from the ages of 0—17 years should be considered for ring 20 chromosome analysis if they have: Genetics[ edit ] Rather ring chromosome 20 the typical linear pattern of a chromosome, deletion of the endings of a chromosome can lead to ring formation. A chromosome has two arms, one long and one short.
Deletion of the short arm of chromosome 20 does not appear to result in epilepsy; however, terminal deletion of the long arm is associated with epilepsy. Therefore, some gene loss from the terminal segment could be responsible for the manifestation of epilepsy in ring chromosome 20 chromosome 20 syndrome.
The most common breakpoint in patients is in the q As chromosomes occur in pairs, the affected individual usually has one normal chromosome and the other replaced by a ring chromosome.
However, this is not usually the case for every cell in the patient. In most individuals with ring chromosome 20 syndrome, a certain percentage have two normal chromosome 20s and the remainder have one normal and one ring 20 chromosome.
ring chromosome 20
This mixture is called mosaicm. A higher degree[ clarification needed ] percentage of mosaicism appears to be associated with earlier age of seizure onset and presence of malformations. Yet, the degree of ring chromosome 20 does not determine response to drug treatment.
Since the range in age of onset of seizures and IQ for a given mosaic ratio is relatively wide, prediction of phenotype based on the mosaicism ratio is somewhat limited. Occasionally, there is a variation, where the ring chromosome 20 syndrome is characterized by an extra ring chromosome in addition to the two normal ones and hence gives rise to a partial trisomy or supernumerary ring This supernumerary ring 20 can cause multiple anomalies but no epilepsy, and this resulting syndrome should ring chromosome 20 differentiated from ring chromosome 20 syndrome.
This confusion has persisted even in the literature.
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