Ring chromosome 20 syndrome
Encyclopedia
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 mental retardation.
When only one copy of chromosome 20 forms a ring, the individual suffers from ring 20 chromosomal mosaicism
.
Chromosome abnormalities
A chromosome anomaly, abnormality or aberration reflects an atypical number of chromosomes or a structural abnormality in one or more chromosomes. A Karyotype refers to a full set of chromosomes from an individual which can be compared to a "normal" Karyotype for the species via genetic testing. A...
where the two arms of chromosome 20
Chromosome 20 (human)
Chromosome 20 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 20 spans around 63 million base pairs and represents between 2 and 2.5 percent of the total DNA in cells...
fuse to form a ring chromosome
Ring chromosome
A ring chromosome is a chromosome whose arms have fused together to form a ring. A ring chromosome is denoted by the symbol r. Ring chromosomes may form in cells following genetic damage by mutagens like radiation, they may also arise spontaneously during development.-Formation:Normally, the ends...
. The syndrome is associated with epileptic seizures
Epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
, behaviour disorders and mental retardation.
When only one copy of chromosome 20 forms a ring, the individual suffers from ring 20 chromosomal mosaicism
Mosaic (genetics)
In genetic medicine, a mosaic or mosaicism denotes the presence of two populations of cells with different genotypes in one individual who has developed from a single fertilized egg...
.