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Spinocerebellar ataxia type 26
A very rare subtype of autosomal dominant cerebellar ataxia type III (ADCA type III) characterized by late-onset and slowly progressive cerebellar signs (gait ataxia) and eye movement abnormalities.
ORPHA:101112Classification level: Disorder
To date, only 23 affected patients have been described from one American family of Norwegian descent.
Spinocerebellar ataxia type 26 (SCA26) onset occurs between the ages of 26-60 with a mean age of onset of 42 years. Slowly progressive gait ataxia and dysarthria were reported in all patients. Nystagmus, impaired pursuit, and dysmetric saccades were described in majority of patitents. Left-sided pyramidal signs (hyperreflexia with positive Babinski sign) were reported in one patient. The disease duration is unknown.
A candidate gene for SCA26 has recently been identified as the eukaryotic translation elongation factor 2 (EEF2) gene, located on chromosome 19p13.3. Further confirmatory studies are still required in order to determine if a mutation in this gene directly causes SCA26.
Diagnosis is based on the clinical findings of pure cerebellar ataxia as well as molecular findings. Head magnetic resonance imaging (MRI) usually demonstrates the presence of atrophy of the cerebellum sparing the brainstem and is helpful in excluding other causes of ataxia. Molecular genetic testing identifies a mutation in the EEF2 gene, confirming a diagnosis of SCA26.
Differential diagnoses include other forms of ADCA type III, in particular SCA5, SCA6, SCA11, SCA30 and SCA31.
Antenatal diagnosis is possible in families with a known disease causing mutation.
SCA26 is inherited autosomal dominantly and genetic counseling is possible. Genetic counseling should be proposed to individuals having the disease-causing mutation informing them that there is 50% risk of passing the mutation to offspring.
Management and treatment
There is no cure for SCA26 and treatment is supportive. Neurological follow-up is recommended to monitor the progression of ataxia.
Disease progression is very slow, but precise prognosis is unknown.
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