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Spinocerebellar ataxia type 5
An autosomal dominant cerebellar ataxia type III that is characterized by the early-onset of cerebellar signs with eye movement abnormalities and a very slow disease progression.
ORPHA:98766Classification level: Disorder
Spinocerebellar ataxia type 5 (SCA5) prevalence is unknown. Five families (American, French, German, and Japanese) with SCA5 have been reported to date.
The mean age of onset is 33 years but it can range from 6 years to 68 years. SCA5 patients clinically present with cerebellar signs (ataxia, dysarthria, tremor), intention tremor, and eye movement abnormalities such as gaze-evoked nystagmus, down beat nystagmus, and impaired smooth pursuit. Occasionally defects of the visual field and horizontal gaze palsy can be also present. Non-cerebellar signs such as facial myokimia, resting tremor, writer's cramp, impaired vibration sense, dysphagia, and brisk deep tendon reflexes have been reported in some patients. SCA5 progresses very slowly with a disease duration of more than 30 years after symptom onset.
SCA5 is caused by mutations in the SPTBN2 gene (11q13.2) encoding beta-III spectrin, a protein essential for the correct functioning and development of Purkinje cells.
Diagnosis is based on the characteristic clinical findings and molecular genetic testing. As the manifestations of SCA5 are not specific, diagnosis is only confirmed with the finding of a mutation in the SPTBN2 gene.
Differential diagnosis includes other types of ADCA (Autosomal dominant cerebellar ataxia).
Antenatal diagnosis is possible in families with a known mutation.
The disease is a rare autosomal dominant spinocerebellar ataxia. 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 SCA5 and treatment is supportive. Physical therapy, as well as the use of canes and walkers, should be offered in order to maximize strength and maintain activity. Wheelchairs are eventually necessary. Speech therapy and communication devices may be useful to those with dysarthria. Dysphagia should be monitored to decrease the risk of aspiration pneumonia. Annual neurological examinations are recommended to monitor disease progression.
Disease progression is slow, but precise prognosis is unknown.
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