Spinocerebellar ataxia type 5 (SCA5) is a rare subtype of autosomal dominant cerebellar ataxia type 3 (ADCA type 3; see this term) characterized by the early-onset of cerebellar signs with eye movement abnormalities and a very slow disease progression.
The prevalence is unknown. Three families (American, French and German) with SCA5 have been reported to date.
The mean age of onset is 33 years but it can range from 10-68 years. SCA5 patients clinically present with cerebellar signs (ataxia, dysarthria, and intention tremor) with 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 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.
SCA5 is inherited autosomal dominantly and genetic counseling is possible.
Last update: November 2014
- Dr Shinsuke FUJIOKA
- Dr Zbigniew WSZOLEK
- Dr Shozaburo YANAMOTO