While pure HSP does not show additional symptoms, symptoms in complicated HSP can also include e.g. mental retardation, epilepsy, cerebellar ataxia, or optic atrophy.[7] SPG31 is one of the most common forms of dominant pure HSP without muscular atrophy or sensory symptoms and is caused by loss‐of‐function variants in REEP1. This evidence concerns the gene REEP1 and cerebellar ataxia.