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17q21.31 microdeletion syndrome
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17q21.31 microdeletion syndromeOn this page:
Reviewed March 2010
What is 17q21.31 microdeletion syndrome?17q21.31 microdeletion syndrome results when a small piece of chromosome 17 is missing. The deletion occurs on the long (q) arm of the chromosome at a location designated q21.31. People with 17q21.31 microdeletion syndrome have developmental delay and intellectual disability. Typically their disposition is described as cheerful, sociable, and cooperative. They usually have weak muscle tone (hypotonia) in childhood. About half have recurrent seizures (epilepsy). Affected individuals often have distinctive facial features including a high, broad forehead; droopy eyelids (ptosis); a narrowing of the eye opening (blepharophimosis); outer corners of the eyes that point upward (upward-slanting palpebral fissures); skin folds covering the inner corner of the eyes (epicanthal folds); a bulbous nose; and prominent ears. They may also have vision problems. Males with 17q21.31 microdeletion syndrome often have undescended testes (cryptorchidism). Defects in the walls between the chambers of the heart (septal defects) or other cardiac abnormalities, kidney problems, and skeletal anomalies such as foot deformities occur in some affected individuals. How common is 17q21.31 microdeletion syndrome?The prevalence of 17q21.31 microdeletion syndrome is estimated to be 1 in 16,000; however, many affected individuals are never diagnosed with this disorder. Researchers estimate that 17q21.31 microdeletion syndrome may account for approximately 6 in 1,000 cases of unexplained intellectual disability. What are the genetic changes related to 17q21.31 microdeletion syndrome?People with 17q21.31 microdeletion syndrome are missing a sequence of about 500,000 DNA building blocks (base pairs), also written as 500 kilobases (kb), at position q21.31 on chromosome 17. The exact size of the deletion varies among affected individuals, but it contains at least six genes. This deletion affects one of the two copies of chromosome 17 in each cell. The signs and symptoms of 17q21.31 microdeletion syndrome are probably related to the loss of one or more genes in this region. Researchers are working to determine how the loss of these genes contributes to the features of 17q21.31 microdeletion syndrome. Read more about chromosome 17. Can 17q21.31 microdeletion syndrome be inherited?The inheritance of 17q21.31 microdeletion syndrome is considered autosomal dominant because a deletion in one copy of chromosome 17 in each cell is sufficient to cause the disorder. Most cases of 17q21.31 microdeletion syndrome are not inherited. The deletion occurs most often as a random event during the formation of reproductive cells (eggs and sperm) or in early fetal development. Affected people typically have no history of the disorder in their family. While it is possible for them to pass the condition on to their children, no individuals with 17q21.31 microdeletion syndrome have been known to reproduce. In all known cases, people with 17q21.31 microdeletion syndrome have at least one parent with a common variant of the 17q21.31 region of chromosome 17 called the H2 lineage. This variant is found in 20 percent of people of European and Middle Eastern descent, although it is rare in other populations. In the H2 lineage, a 900 kb segment of DNA including the region deleted in 17q21.31 microdeletion syndrome has undergone an inversion. An inversion involves the breakage of a chromosome in two places; the resulting piece of DNA is reversed and reinserted into the chromosome. People with the H2 lineage have no health problems related to the inversion. However, genetic material can be lost or duplicated when the inversion is passed to the next generation. Researchers believe that a parental inversion is probably necessary for a child to have 17q21.31 microdeletion syndrome, but other, unknown factors are also thought to play a role. So while the inversion is very common, only an extremely small percentage of parents with the inversion have a child affected by 17q21.31 microdeletion syndrome. Where can I find information about diagnosis or management of 17q21.31 microdeletion syndrome?These resources address the diagnosis or management of 17q21.31 microdeletion syndrome and may include treatment providers.
You might also find information on the diagnosis or management of 17q21.31 microdeletion syndrome in Educational resources and Patient support. General information about the diagnosis and management of genetic conditions is available in the Handbook. To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook. Where can I find additional information about 17q21.31 microdeletion syndrome?You may find the following resources about 17q21.31 microdeletion syndrome helpful. These materials are written for the general public.
You may also be interested in these resources, which are designed for healthcare professionals and researchers.
What other names do people use for 17q21.31 microdeletion syndrome?
For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines and How are genetic conditions and genes named? in the Handbook. What if I still have specific questions about 17q21.31 microdeletion syndrome?Where can I find general information about genetic conditions?The Handbook provides basic information about genetics in clear language.
These links provide additional genetics resources that may be useful. What glossary definitions help with understanding 17q21.31 microdeletion syndrome?autosomal ; autosomal dominant ; base pair ; blepharophimosis ; cardiac ; cell ; chromosome ; cryptorchidism ; deletion ; developmental delay ; DNA ; egg ; epicanthal fold ; gene ; hypotonia ; inheritance ; inversion ; kb ; kidney ; kilobase ; lineage ; microdeletion syndrome ; monosomy ; muscle tone ; population ; prevalence ; ptosis ; reproductive cells ; seizure ; septal defect ; sign ; sperm ; symptom ; syndrome ; testis You may find definitions for these and many other terms in the Genetics Home Reference Glossary. See also Understanding Medical Terminology.
References (6 links)
The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook. |