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Spinocerebellar Ataxia Type 3 (SCA3)

Name of disease:

Spinocerebellar Ataxia Type 3 (SCA3)

ICD-10 diagnosis code:

G11.8

Causes:

Mutations in the ATXN3 gene cause SCA3.
The ATXN3 gene mutations that cause SCA3 involve a DNA segment known as a CAG trinucleotide repeat. This segment is made up of a series of three DNA building blocks (cytosine, adenine, and guanine) that appear multiple times in a row.
Normally, the CAG segment is repeated 12 to 43 times within the gene. Most people have fewer than 31 CAG repeats. In people with SCA3, the CAG segment is repeated more than 50 times.
An increase in the length of the CAG segment leads to the production of an abnormally long version of the ataxin-3 enzyme that folds into the wrong 3-dimensional shape. This nonfunctional ataxin-3 enzyme cannot remove ubiquitin from proteins that are no longer needed.
As a result, these unwanted proteins along with ubiquitin and ataxin-3 cluster together to form clumps within the nucleus of the cells.
It is unclear how these aggregates affect cell function because they are found in healthy cells as well as those that die.

Mode of inheritance:

SCA3 is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.
In most cases, an affected person has one parent with the condition.

Prevalence:

1-5 in 100,000

Diagnosis:

Genetic test

Age of onset:

The age of onset varies greatly from 10 to 70 years of age

Common signs and symptoms:

Balance problems (ataxic gait)
Incoordination of hands
Slurred speech (dysarthria)
Some problems with blurred vision (due to problems with eye movement)
Problems with swallowing, stiffness, muscle spasms, or a reduced ability to discriminate temperature

Available treatment (medicinal and non-medicinal):

Physiotherapy
Speech therapy
Occupational therapy
Medications for problems with sleeping, muscle spasms, or Parkinson's disease-like symptoms

Disease management tips:

Safety measures are needed to avoid falls at home as the disease progresses
Patients experiencing falls should be evaluated for appropriate assistive devices by healthcare providers

References:

Other useful websites:

Hong Kong Spinocerebellar Ataxia Association