SPG11 and Alzheimer disease: Importantly, the similarities and overlapping of some genes implicated in the common NDDs—ALS, AD and PD—which were studied in this paper, and HSP have been reported [62,63]; especially type 11 HSP (with mutation in SPG11 gene) showed pathological similarities with ALS [64], while a small percentage of HSP patients displayed PD-specific symptoms in the dopamine transmission impairment [65].