What kind of mutation is Canavan Disease?

For a project, i can't find it online.

Is it:






1 Answer

  • 9 years ago
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    this is about all the info i could find Canavan disease belongs to a group of conditions known as leukodystrophies, which result from defects in myelin. Myelin, a substance made up of proteins and lipids, is an integral component of the nervous system. It is commonly known as the "white matter" in the brain; its function is to protect nerves and allow messages to be sent to and from the brain. In Canavan disease the white matter deteriorates because affected children have a deficiency of the enzyme aspartoacylase, which leads to the accumulation of a chemical, called N-acetyl-aspartic acid (NAA), in the brain. It is not known exactly how this chemical imbalance causes the destruction of myelin but all of the symptoms of Canavan disease can be explained by this progressive loss of myelin.Canavan disease, like Tay-Sachs, is inherited as an autosomal recessive trait. Both of the parents of an affected child are carriers of an altered gene on chromosome 17 that is responsible for synthesizing aspartoacylase. A parent who is a carrier is healthy because he or she has one functional copy of the gene that produces a sufficient amount of the enzyme. A child who receives two altered copies of the gene, one from each parent, is unable to produce any aspartoacylase and will develop the symptoms of Canavan disease.

    Carrier Testing

    Canavan disease is most commonly found in people of Ashkenazi Jewish descent, although it is also seen in other ethnic groups. Biochemical tests for aspartoacylase activity are not sensitive enough to detect carriers, but DNA testing of Ashkenazi Jewish couples can tell with over 95% certainty whether either or both parents is a carrier. If neither or only one parent carries a mutation in the aspartoacylase gene, the couple is not at risk for having a child with Canavan disease. If both parents are carriers, there is a 25% chance with each pregnancy that their child will have Canavan disease. Genetic counseling is important to assist at-risk couples in exploring their options in planning their families. Accurate and reliable DNA-based prenatal testing, using samples obtained through CVS or amniocentesis, is available to couples who are both carriers of identified mutations.

    In situations where at least one parent is not of Ashkenazi Jewish ancestry, DNA testing may be less informative. Many of the DNA mutations that cause Canavan disease in children of other ethnic backgrounds are unique to individual families. In situations where a non- Ashkenazi individual has a family history of Canavan disease, it may be possible to identify the mutation in that family and use the information for prenatal diagnosis. However, identifying individual mutations is costly and time-consuming and requires initiative on the part of the individuals seeking the information since it is not routinely done. Another method of prenatal diagnosis which may provide information to families with unidentified mutations is linkage analysis, a form of DNA testing which compares the DNA of the fetus to that of affected and unaffected relatives to determine whether the fetus is likely to be affected. A third method relies on the measurement of NAA levels in amniotic fluid; accurate determination of NAA levels in amniotic fluid is difficult and is only performed at one or two laboratories in the U.S.

    Assisted reproductive technologies are also available to at-risk couples who wish to have children but for whom abortion is not an option. One option available to them is artificial insemination by a non-carrier sperm or egg donor. Another option, available only for couples with identified DNA mutations in the ASPA gene, is preimplantation genetic diagnosis.

    Because of the severity of Canavan disease, the lack of treatment for it, and its high incidence in the Ashkenazi Jewish population, the American College of Obstetricians and Gynecologists adopted a position statement in 1998 recommending that all Ashkenazi Jewish individuals, either contemplating a pregnancy or already pregnant, be offered carrier testing for Canavan disease by their physician. Population screening within the Jewish community is now being offered as well, using the model developed for population screening for Tay-Sachs disease. As was done earlier for Tay-Sachs disease, it is important that population-based screening be coupled with thorough education and genetic counseling services so that test results are interpreted correctly. http://ghr.nlm.nih.gov/condition/canavan-disease http://www.ncbi.nlm.nih.gov/books/NBK1234/

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