The primary pathophysiological feature of the disease is a “dying back type” axonal neuropathy that primarily affects upper motor neurons of the pyramidal tract.1, 2 Collectively, more than 80 genes and at least 76 linkage loci have been associated with HSP.3, 4 Among all of these genes, mutations in SPAST, ATL1, SPG7, and SPG11 remain the most prevalent causes of HSP. The gene discussed is SPAST; the disease is hereditary spastic paraplegia.