This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
Ring chromosome 21 is a rare chromosome abnormality in which the ends of chromosome 21 join together to form a ring shape. Many people with ring chromosome 21 have normal development and are healthy, having been diagnosed after having chromosome testing due to infertility, multiple miscarriages, or a child with a chromosome abnormality. However, others with ring chromosome 21 have developmental and/or medical problems which can range from mild to severe. This is due to having extra or missing genetic material on the ring chromosome, which can happen when the ring chromosome forms. Signs and symptoms of ring chromosome 21 that may be present can include short stature, delayed puberty in males, small head size, seizures, learning disabilities, underdeveloped sex organs, susceptibility to infections, and/or a variety of birth defects. Some people have signs and symptoms similar to those that occur in people with Down syndrome.
Ring chromosome 21 may be inherited from a parent (typically the mother), or it may occur sporadically (by chance) during the formation of egg or sperm cells or shortly after the egg and sperm join together. A chromosome test of the parents can help determine whether it was inherited and whether future children have an increased chance to have a chromosome abnormality. Treatment for ring chromosome 21 depends on the signs and symptoms present in each person.
For more information, visit GARD.