It accounts for 17–79% of AD HSP cases with monoallelic forms of KIF1A variant carriers, SPG3A and SPG31 coming next (Schüle et al., 2016; Burguez et al., 2017; Dong et al., 2018; Boutry et al., 2019a; Méreaux et al., 2021b). Here, REEP1 is linked to Alzheimer disease.