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National Ataxia Foundation FAQ
FREQUENTLY ASKED QUESTIONS ABOUT...
Spinocerebellar Ataxia Type 8 (SCA8)
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| What is spinocerebellar ataxia type 8? |
Spinocerebellar ataxia type 8 (SCA8) is one
type of ataxia among a group of inherited
diseases of the central nervous system. As in
other inherited ataxias, SCA8 is the result of
genetic defects that lead to impairment of
specific nerve fibers carrying messages to and
from the brain, resulting in degeneration of
the cerebellum (the coordination center of the
brain).
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| What are the symptoms of SCA8? |
Typically, balance and coordination problems
(ataxia) are noticed first. Often there is
accompanying muscle spasticity, slurred
speech, and reduced vibration sense. As the
disease progresses over a period of several
years, difficulty swallowing and other
symptoms are experienced.
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| How is SCA8 acquired? |
SCA8 is a genetic disorder, which means that
it is an inherited disease. The abnormal gene
responsible for this disease is passed along
from generation to generation by family
members who carry it. Genetic diseases occur
when one of the body’s 100,000 genes does
not work properly. (Genes are microscopic
structures within the cells of our bodies that
contain instructions for every feature a
person inherits from his or her parents.)
The gene responsible for SCA8 is located
on chromosome 13 (each person has 23 pairs
of chromosomes). Genes are made up of
substances known as nucleotides linked
together in chains. Each nucleotide is identified
by a letter. In SCA8, a gene mutation
on chromosome 13 results in extra copies of
a series of nucleotides identified by the letters
C-T-G. (Other identified forms of SCA are
caused by extra copies of a C-A-G series.)
SCA8 is more complex genetically than
other SCAs in that it can appear to be
dominant, recessive, or sporadic. A hereditary
ataxia is considered dominant if only one copy
of the defective gene needs to be inherited in
order to develop the disease, and recessive if
two copies of the defective gene (one from
each parent) are required to develop the
disease. In cases of sporadic hereditary
ataxia, there is no known family history of
the disease.
SCA8 acts like a dominant ataxia in that a
person needs to inherit only one copy of the
defective gene in order to develop the disease,
but often family trees indicate a sporadic or
recessive pattern to the disease. Whereas
dominant diseases will typically affect several
individuals in each generation, SCA8 often
appears when there has been no family
history of the disease. Research has shown
that the SCA8 gene is unstable, and therefore
acts differently from other dominant ataxias.
When the unstable SCA8 gene is passed on
by a mother who is unaffected by the disease,
the number of C-T-G repeats can expand and
cause disease in her children. On the other
hand, when this gene is passed on by a father
who is affected by the disease, the C-T-G
repeats might decrease so that the children are not affected. This unique aspect
of SCA8 helps explain why some family
members can inherit the abnormal gene but
not develop the disease, and why family trees
do not always show a clear dominant disease
pattern.
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| How common is SCA8? |
SCA8 is a relatively rare form of ataxia; its
occurrence is less than 1/100,000.
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| How is the diagnosis made? |
A neurologist is often the most helpful
specialist in recognizing symptoms and
diagnosing the diseases that cause ataxia.
Initially, a neurologic examination can
determine whether a person has symptoms
typical of one of the SCAs. DNA-based testing
can determine the presence or absence of the
abnormal gene that causes SCA8. However,
the nature of the SCA8 gene makes the
diagnosis more complex than in other SCAs.
Research indicates that the length of the
C-T-G repeat determines whether or not a
person will develop ataxia. People with fewer
than 100 C-T-G repeats on the SCA8 gene
tend not to develop the disease, while those
with more than 110 C-T-G repeats are likely
to get the disease. An unusual feature of the
SCA8 gene is that when the number of
C-T-G expansions becomes too large (more
than 250), the gene no longer appears to
cause disease. However, when a father who
has a gene with such a large expansion passes
it to his children, it can once again contract
in the children and cause the disease to
appear in them.
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| What kind of support is available
after the diagnosis? |
Although there is no specific treatment to
delay or halt the progression of the SCAs,
there is supportive therapy available to help
manage symptoms, and there are resources
to provide emotional support. Living With
Ataxia: An Information and Resource Guide,
published by the National Ataxia Foundation,
includes a range of practical information and
lists additional resources. NAF also provides
and participates in many support and chat
groups on the Internet. Visit our Web site (see
address below) for a listing of these groups.
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National Ataxia Foundation
2600 Fernbrook Lane, Suite 119
Minneapolis, MN 55447-4752
Phone: (763) 553-0020
Fax: (763) 553-0167
E-mail: naf@ataxia.org
Website: www.ataxia.org
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SCA8 FAQ |
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