SACS and cerebellar ataxia: Mutations in SACS cause autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS), a disorder characterised by the triad of cerebellar ataxia, peripheral neuropathy, and spasticity; however not all features of the triad may be present and there is a phenotypic overlap with the AR HSP with a thin corpus callosum (AR-HSP-TCC) [29].