染色體結構變異 之環(huán)狀染色體

1、之 環(huán)狀染色體 染色體結構畸變洛冰發(fā)病機制疾病簡介環(huán)狀染色體環(huán)狀染色體一條染色體的長短臂同時發(fā)生了斷裂，含有著絲粒的片段兩斷端發(fā)生重接，即形成環(huán)狀染色體。發(fā)病機制：46,XX(XY),r(2)(p21q31);46,XX(XY),r(2)(p21q31);46,XX(XY),r(2)(p21q31);46,XX(XY),r(2)(p21q31);發(fā)病機制疾病簡介環(huán)狀染色體環(huán)狀染色體 2 Epilepsy & Seizures 3 Diagnosis 4 Genetics 5 Treatment 1 profile ring-shaped chromosome 201 profilering-s

2、haped chromosome 20 or r(20) syndrome is a rare human chromosome abnormality where the two arms ofchromosome 20 fuse to form a ring chromosome. The syndrome is associated with epileptic seizures, behaviour disorders and mental retardation.When not all cells contain a ring chromosome 20, the individu

3、al suffers from 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 unre

4、cognized.2 Epilepsy & SeizuresRecurrent 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

5、 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

6、 these complex partial seizures include staring, oral automatisms, unspecified automatic behavior, involuntary motor movements and/or head turning.3 DiagnosisThe ring 20 abnormality may be limited to as few as 5% of cells, so a screen for chromosomal mosaicism is critical. Newer array technology wil

7、l not detect the ring chromosome and the standard metaphase chromosome analysis has been recommended. A karyotype analysis examining at least 50 cells should be requested to properly detect mosaicism.4 GeneticsRather than the typical linear pattern of a chromosome, deletion of the endings of a chrom

8、osome 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

9、responsible for the manifestation of epilepsy in ring chromosome 20 syndrome. The most common breakpoint in patients is in the q13.33 region of chromosome 20. 5 TreatmentKetogenic DietEpilepsy SurgeryVNS TherapyKetogenic DietThe ketogenic diet is a high fat, low carbohydrate diet reserved for intrac

10、table childhood epilepsies. There are no published reports on the use of the ketogenic diet in patients with ring chromosome 20 syndrome. However, its efficacy and safety are well established in other difficult to control epilepsy syndromes.Epilepsy SurgeryEpilepsy surgery investigations are perform

11、ed to identify a discrete seizure focus. Extensive investigations in ring chromosome 20 syndrome patients fails to identify a discrete seizure focus and published data supports that that epilepsy in ring chromosome 20 syndrome is not amenable to resective surgery.VNS TherapyThe vagal nerve stimulator is a battery-powered device similar to a pacemaker that is implanted under the skin. It delivers a mild electrical stimulation to the brain via the vagus nerve and has proven to be effective for the treatment of complex