Mutations in the spastic paraplegia genes SPG11, encoding spatacsin, and ZFYVE26, encoding Spastizin (SPG15), cause the most prevalent forms of autosomal-recessive hereditary spastic paraplegia with thinning of the corpus callosum (AR-HSP-TCC) [46,47,48,49]. The gene discussed is SPG11; the disease is hereditary spastic paraplegia.