Spinocerebellar Ataxia (SCA)
Last updated November 2010
Spinocerebellar ataxia (SCA) is one of a group of genetic disorders
characterized by slowly progressive in-coordination of gait and often
associated with poor coordination of hands, speech, and eye
movements. Frequently, atrophy of the cerebellum occurs. As with
other forms of ataxia, SCA results in unsteady and clumsy motion of
the body due to a failure of the fine coordination of muscle
movements, along with other symptoms.
The symptoms of the condition vary with the specific type (there are
several), and with the individual patient. Generally, a person with
ataxia retains full mental capacity but may progressively lose
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If the disease is caused by a polyglutamine
trinucleotide repeat CAG expansion, a longer expansion may lead to
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an earlier onset and a more radical progression of clinical
It can be easily misdiagnosed as another neurological condition,
such as multiple sclerosis (MS). One means of identifying the
disease is with an MRI to view the brain. Once the disease has
progressed sufficiently, the cerebellum (a part of the brain) can be
seen to have visibly shrunk. The most precise means of identifying
SCA, including the specific type, is through DNA analysis. Some, but
far from all, types of SCA may be inherited, so a DNA test may be
done on the children of a person with the condition, to see if they
are at risk of developing the condition.
SCA is related to olivopontocerebellar atrophy (OPCA); SCA types 1,
2, and 7 are also types of OPCA. However, not all types of OPCA are
types of SCA, and vice versa. This overlapping classification system
is both confusing and controversial to some in this field.
The following is a list of some, not all, types of spinocerebellar
ataxia. The first ataxia gene was identified in 1993 for a dominantly
inherited type. It was called Spinocerebellar ataxia type 1" (SCA1).
Subsequently, as additional dominant genes were found they were
called SCA2, SCA3, etc. Usually, the "type" number of "SCA" refers
to the order in which the gene was found. At this time, there are at
least 29 different gene mutations which have been found (not all
Identifying the different types of SCA now requires knowledge of
the normal genetic code, and faults in this code, which is contained
in a person's DNA (Deoxyribonucleic acid). The "CAG" mentioned
below is one of many three-letter sequences that makes up the
genetic code. Thus, those ataxias with poly CAG expansions, along
with several other neurodegenerative diseases resulting from a poly
CAG expansion, are...