Similarly, Aldehyde Dehydrogenase 18 Family Member A1 (SPG9B/ALDH18A1) and Ectonucleoside triphosphate diphosphohydrolase 1 (SPG64/ENTPD1) at q24.1 are shown to cause AR HSP [30,51]. The gene discussed is ENTPD1; the disease is hereditary spastic paraplegia.