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A ring chromosome is a chromosome with ends which have fused, creating a ring shape. Surprisingly, the distortion in shape is actually not a problem; the genetic information on the chromosome is still perfectly readable even if the arms are bent in a ring. The issue is that genetic information is often moved or deleted when a ring chromosome forms, and as a result, the genes on that chromosome may not express properly. This can lead to health problems which range from congenital conditions to cancer.
The mechanism through which a ring chromosome forms is not fully understood. In some cases, the ends appear to fuse with no changes to the genetic material inside. In other cases, one or both ends is snipped off, and the ends of the chromosome fuse. Ring chromosomes are fairly rare, but they do happen, even without a clear mechanism for their formation. Some researchers are interested in learning more about how, when, and why they form, with the goal of preventing some conditions caused by this type of chromosomal abnormality.
Commonly, ring chromosomes form as spontaneous mutations in response to toxins, radiation, and similar types of exposure. Sometimes, the result is a defective cell which dies because it cannot survive. In other cases, a cell can become malignant or abnormal as a result of a ring chromosome, and this could lead to the development of a larger abnormalities. Ring chromosomes have been observed in some cancerous tumors, for example.
Ring chromosomes can also arise during development. In some cases, this can lead to genetic disorders such as Turner Syndrome, in which one of the X chromosomes is a ring chromosome, along with ring chromosomes 14 and 15, which can cause developmental delays. This defect at chromosome 20 can sometimes lead to a form of epilepsy. Genetic testing will reveal the chromosomal abnormality, and detailed testing can be used to learn more about which genetic information was deleted or mangled when the ring chromosome formed.
Some people have ring chromosomes in their bodies and remain unaware of it, while in other cases, a suspected ring chromosome may be identified shortly after birth. The diversity of the spectrum from profound developmental delays to a blissfully unaware existence illustrates the diversity of human genetics, and the fact that the chromosomes are actually much more active in the body than was once thought. Historically, people believed that the chromosomes remained static throughout life, but evidence has shown that chromosomes in various regions of the body actually do change, sometimes quite radically.