Probands will be recruited at the HSP Outpatient Clinic of the Department of Neurology in Tübingen. Eligible participants are age 18 to 70 years of age. Group 1 include p: patients with genetically confirmed SPG4 (group 1) and manifest disease with spastic gait disorder. Group 2 includes age- and sex-matched and healthy controls (spouses, other relatives or further healthy controls) with an educational level comparable to group 1 (group 2).