SACS and Charlevoix-Saguenay spastic ataxia: We have previously shown that sacsin is almost absent or strikingly reduced in fibroblasts of patients with ARSACS, regardless of the nature of the SACS genetic variant.7 This applies not only to patients with ARSACS carrying truncating variants, as expected, but also to patients who are compound heterozygotes either for two diverse SACS pathogenic missense variants, or for a missense variant and a truncating SACS variant.