REEP1 and muscular atrophy: 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.