Now identified as one of the most common causes of HSP, SPG7-associated disease has been linked to additional neuro-ophthalmologic features, including isolated dominant optic atrophy, cerebellar eye signs (various forms of nystagmus, dysmetric saccades), progressive external ophthalmoplegia (PEO), and supranuclear vertical palsy. This evidence concerns the gene SPG7 and progressive external ophthalmoplegia.