Spinocerebellar Ataxia Type 1

Spinocerebellar Ataxia Type 1

  • Spinocerebellar ataxia type 1 (SCA1) is a subtype of type I autosomal dominant cerebellar ataxia (ADCA type I; see this term) characterized by dysarthria, writing difficulties, limb ataxia, and commonly nystagmus and saccadic abnormalities.




How common is Spinocerebellar Ataxia Type 1?

  • 1-9/100000
  • Prevalence is estimated to be 1-2 in 100,000 with significant geographical and ethnic variations.


Autosomal dominant 

Age of Onset

All ages

What causes SCA1?

SCA1 is caused by CAG repeat expansions in the ATXN1 gene region on chromosome 6p23.

What are the symptoms of Spinocerebellar Ataxia Type 1?

  • The disease typically presents in the 4th decade (age range = 4-74 years).
  • Ataxia gradually progresses and additional features may emerge including proprioceptive loss, hypoactive reflexes, ophthalmoparesis, and mild optic neuropathy. Initial presentation with blepharospasm, oromandibular dystonia, and retrocollis preceding ataxia has been reported. Cognition is relatively spared early on; however, executive dysfunction and impaired verbal memory may develop in later stages.

Very Common Symptoms

  • Peripheral neuropathy 
  • Progressive cerebellar ataxia

Common Symptoms

  • Abnormal flash visual evoked potentials
  • Abnormal nerve conduction velocity
  • Abnormality of eye movement
  • Abnormality of somatosensory evoked potentials 
  • Atrophy/Degeneration affecting the brainstem
  • Bradykinesia
  • Bulbar signs
  • Cerebellar atrophy 
  • Chorea
  • Cognitive impairment
  • Dysarthria
  • Dysphagia
  • Dystonia
  • Gait disturbance
  • Inertia
  • Loss of Purkinje cells in the cerebellar vermis
  • Memory impairment
  • Slow saccadic eye movements
  • Slurred speech
  • Staring gaze
  • Upgaze palsy

Occasional Symptoms

  • Abnormal brainstem morphology
  • Abnormality of masticatory muscle
  • Dysdiadochokinesis
  • Dysmetria
  • Fasciculations
  • Gait imbalance
  • Generalized hypotonia
  • Hyperactive deep tendon reflexes
  • Hypermetric saccades
  • Hyporeflexia
  • Impaired proprioception
  • Nystagmus
  • Ophthalmoparesis
  • Optic atrophy
  • Postural tremor
  • Respiratory failure
  • Skeletal muscle atrophy 

What is the prognosis?

  • Prognosis is poor.
  • In the late stages of the disease, usually 10 to 15 years following onset, bulbar dysfunction secondary to affection of lower medullary nuclei results in aspiration which is life-threatening.


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