SACS and neurodegenerative disease: Autosomal recessive spastic ataxia of Charlevoix–Saguenay (ARSACS) is a rare, childhood- to adult-onset neurodegenerative disease characterized by progressive ataxia, spasticity and neuropathy.1 It is caused by pathogenic variants in the SACS gene encoding for sacsin, a 520-kDa multimodular protein whose function is still poorly understood.