• Clinical science

Spinocerebellar ataxia

Abstract

Spinocerebellar ataxia (SCA) refers to a group of progressive neurodegenerative diseases of genetic origin. Currently, more than 30 types have been identified, most of which are autosomal dominant, such as SCA3. Trinucleotide repeat expansions in a disease-associated protein (e.g., CAG repeats in ataxin-1) are commonly the underlying genetic anomaly. Patients usually present between the ages of 30–50 with slowly progressive symptoms of cerebellar ataxia, including incoordination of gait, hand, speech, and eye movements. The diagnosis is reached on the basis of family history and neurological examination, but neuroimaging and molecular genetic testing help identify the specific cause and type of SCA. To date, there is no effective treatment. Therapy is directed towards alleviating symptoms. The prognosis depends on individual genetic properties, but most patients progressively develop severe, irreversible disability, while retaining full mental capacity, within 15 years of symptom onset.

Epidemiology

  • Prevalence: ∼ 1–4/100,000
  • Age of onset: 30–55 years
  • Most common type (worldwide): SCA3

References:[1][2]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

References:[3][4][5]

Clinical features

  • Features common to all types of SCA:
    • Cerebellar ataxia
      • Progressive gait ataxia; (usually broad-based)
      • Progressive limb ataxia; including tremor
      • Nystagmus
    • Dyssynergia , dysmetria; , dysdiadochokinesia; , and/or dysarthria may be present.
  • Further clinical features :
Type of ADCA Important SCA types Clinical features
Type I SCA1­–SCA4, SCA8, SCA10, SCA12–SCA23, SCA25, SCA27, SCA28
Type II SCA7
  • Ataxia
  • Pigmentary maculopathy and subsequent blindness
Type III SCA5, SCA6, SCA11, SCA26, SCA29, SCA30, and SCA31
  • Only ataxia; usually late onset

References:[4]

Treatment

There is currently no effective causative therapy available and therefore treatment focuses on symptom management.

  • Canes, braces, and wheelchairs for gait ataxia
  • Use of special devices to assist with fine movements (e.g., handwriting, buttoning clothes, use of eating utensils)
  • Speech therapy for dysarthria and severe speech deficits

References:[1][4]

Diagnostics

The diagnosis is clinical and based on family history and neurological examination. Further tests help identify the specific cause and type of SCA.

  • Neuroimaging (CT/MRI): cerebellar atrophy is a finding common to all SCAs
  • Molecular genetic testing: precise identification of SCA type

Prognosis

  • Variable for each SCA type, but generally poor