ARSACS is caused by mutations in the SACS gene, which encodes sacsin, a 520 kDa modular protein containing, from the N- to C-terminus, a ubiquitin-like (UbL) domain that binds to the proteasome [2], three large sacsin repeat regions (SRRs) that may have an Hsp90-like chaperone function [3], a J-domain that binds Hsp70 [2,4], and a higher eukaryotes and prokaryotes nucleotide-binding (HEPN) domain that can dimerise [2,3,4,5,6]. This evidence concerns the gene SACS and Autosomal recessive spastic ataxia of Charlevoix-Saguenay.