染色体结构变异 之环状染色体

03
VNS Therapy
The 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 partial seizures. There are only a few published reports on the success of this therapy in ring chromosome 20 epilepsy syndrome, making it unclear if this is the optimal therapy.
The end
染色体 结构畸变
洛冰
环状染色体
发病机制
疾病简介
发病机制：
2p2 1
一条染色体的长短臂同时发生了 断裂，含有着丝粒的片段两断端 发生重接，即形成环状染色体。
2q3 1
环状染色体(ring chromosome，r)
2p2 1
p21 q31
2q3 1
46,XX(XY),r(2)(p21q31); 46,XX(XY),r(2)(p21→q31);
•3 Diagnosis
The ring 20 abnormality may be limited to as few as 5% of cells, so a screen for chromosomal mosaicism is critical. Newer array technology will 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.
02
Epilepsy Surgery
Epilepsy surgery investigations are performed 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.
• 5 Treatment
01
Ketogenic Diet
02
Epilepsy Surgery
03
VNS Therapy
01
Ketogenic Diet
The ketogenic diet is a high fat, low carbohydrate diet reserved for intractable 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.

环状染色体(ring chromosome，r)
环状染色体(ring chromosome，r)
环状染色体
发病机制
疾病简介
ring-shaped chromosome 20
• 3 Diagnosis
• 2 Epilepsy & Seizures
• 4 Genetics
• 1 profile
• 5 Treatment
•2 Epilepsy & Seizures
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.
•4 Genetics
Rather than 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 syndrome. The most common breakpoint in patients is in the q13.33 region of chromosome 20.
•1 profile
ring-shaped 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 individual 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 unrecognized.