Clinical Reference · Movement Disorders

SCA3

Machado-Joseph disease — the most common dominant ataxia worldwide
Illustration of a patient with ataxia and bulging eyes
Ataxia + bulging eyes
AD polyglutamine (CAG)
GeneATXN3 (ataxin-3) · 14q32
MutationCAG repeat (polyglutamine)
anticipation
InheritanceAutosomal dominant
OnsetAdult, 30s–50s (variable)
Adult-onset dominant cerebellar ataxia with bulging eyes and faciolingual fasciculations.
Key clinical features
  • Progressive cerebellar ataxia
  • Ophthalmoplegia + lid retraction (bulging eyes)
  • Faciolingual fasciculations / myokymia
  • Dystonia & parkinsonism
  • Spasticity, peripheral neuropathy
  • Restless legs, autonomic signs
◆ Signature clue

Adult-onset dominant ataxia + bulging eyes + faciolingual fasciculations → SCA3 (Machado-Joseph) — the most common SCA worldwide.

Diagnosis
ATXN3 CAG-repeat testing. MRI: pontine & cerebellar atrophy.
Management
Supportive — PT; levodopa may help parkinsonism; treat RLS, spasticity, neuropathic pain.
Board pearlMost common spinocerebellar ataxia worldwide; a polyglutamine CAG disease — remember the bulging eyes.
Sources: Neuro.Wiki › Movement Disorders / SCA3 (Machado-Joseph). Educational reference — not a substitute for clinical judgment. Neuro.Wiki