SPG11 accounts for <1 % of patients with a pure phenotype, 4.5 % of cases with spastic paraplegia and cognitive impairment without thinning of the corpus callosum (TCC), but up to 59 % of persons with early-onset progressive spasticity with mild intellectual disability and/or cognitive decline associated with TCC. The gene discussed is SPG11; the disease is Spastic paraplegia.