The following information may help to address your question:
How is spinocerebellar ataxia 2 inherited?
2 (SCA2) is inherited
in an autosomal dominant
manner. This means that having one changed (mutated
) copy of ATXN2
(the responsible gene
) in each cell
is enough to cause signs and symptoms of the condition.
gene mutations that cause SCA2 involve a DNA sequence
called a 'CAG trinucleotide repeat
.' It is made up of a series of three DNA
building blocks (CAG stands for cytosine
, and guanine
) that appear multiple times in a row. The CAG sequence is normally repeated about 22 times in the gene, but it can be repeated up to 31 times without causing health problems. SCA2 develops in people who have 32 or more CAG repeats in the ATXN2
In most cases, an affected person inherits the mutated gene (with too many repeats) from an affected parent. However, in some cases, an affected person does not have an affected parent. People with an increased number of CAG repeats who don't develop SCA2 are still at risk of having children who will develop the disorder. This is because as the gene is passed down from parent to child, the number of CAG repeats often increases. In general, the more repeats a person has, the earlier symptoms begin. This phenomenon is called anticipation
. People with 32 or 33 repeats tend to develop symptoms in late adulthood, while people with more than 45 repeats often have symptoms by their teens. For some reason, the number of repeats tend to increase more when the gene is inherited from a person's father than when inherited from a person's mother.
Each child of an affected person has a 50% chance of inheriting the CAG repeat expansion.
Last updated: 6/24/2014
How is spinocerebellar ataxia 2 diagnosed?
Molecular genetic testing
(analysis of DNA) is needed for a diagnosis of spinocerebellar ataxia 2 (SCA2). This testing detects abnormal CAG trinucleotide repeat expansions in the ATXN2
gene. Affected people (or people who will later develop symptoms of SCA2) have a copy of the ATXN2
gene that has 33 or more CAG repeats. This testing detects nearly 100% of cases of SCA2.
Last updated: 1/17/2017
How do I know if my children are at risk of developing spinocerebellar ataxia 2?
Each child of a person with a CAG repeat expansion that causes SCA2 has a 50% chance of inheriting the repeat expansion. Molecular genetic testing of the ATXN2
gene is the only way to determine with certainty if a person has SCA2 or will develop SCA2. The presence or absence of symptoms at a given age cannot be used to predict whether a person has inherited a CAG repeat expansion from a parent.
Testing for the mutation that causes a disease in the absence of definite symptoms of the disease is called predictive testing
. When a family member has been diagnosed with SCA2 by genetic testing, predictive testing is available for adults in the family who show no signs of the condition (are asymptomatic). However, this testing is not useful in predicting the age of onset, severity, type of symptoms, or rate of progression in asymptomatic people. Predictive testing for adult family members usually involves pre-test interviews regarding the motives for wanting the test, the person's knowledge of SCA2, neurologic status, and the possible impact of positive and negative test results.
There is general consensus among the medical community that people younger than age 18 who are at risk for adult-onset disorders should not have testing in the absence of symptoms. The main arguments against this testing are that it removes the person's choice to know or not know this information; it raises the possibility of stigmatization within the family and in other social settings; and it could have educational and career implications. However, people younger than age 18 who are symptomatic usually benefit from having a specific diagnosis.
People interested in learning about the risk of developing SCA2 for themselves or family members should speak with a genetics professional.
Last updated: 1/17/2017
If I did not inherit spinocerebellar ataxia 2 from a parent, are my children still at risk?
If a person does not inherit the disease-causing mutation from a parent with SCA2, their children are not at risk for having that mutation.
Last updated: 6/23/2014
How can I find a genetics professional in my area?
Last updated: 12/6/2017
We hope this information is helpful. We strongly recommend you discuss this information with your doctor. If you still have questions, please
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