Additional symptoms such as cognitive impairment, cerebellar ataxia, epilepsy, retinal degeneration, lower motor neuron damage, and thinning of the corpus callosum characterise spastic paraplegia type-11 (SPG11 or also known as KIAA1840) and spastic paraplegia type-15 (SPG15). This evidence concerns the gene SPG11 and retinal degeneration.