▁the ▁disease ▁is ▁slower ▁to ▁progress ▁and ▁life ▁expect ancy ▁is ▁less ▁than ▁the ▁health y ▁population . ▁Death ▁before ▁the ▁age ▁of ▁ 2 0 ▁is ▁frequent , ▁although ▁many ▁people ▁with ▁S MA ▁live ▁to ▁become ▁parents ▁and ▁grand par ents . ▁S MA ▁type ▁III ▁has ▁normal ▁or ▁near - normal ▁life ▁expect ancy ▁if ▁standards ▁of ▁care ▁are ▁followed . ▁Type ▁IV , ▁adult - ons et ▁S MA ▁usually ▁means ▁only ▁mob ility ▁imp air ment ▁and ▁does ▁not ▁affect ▁life ▁expect ancy . ▁ ▁Research ▁directions ▁ ▁Since ▁the ▁underlying ▁gen etic ▁cause ▁of ▁S MA ▁was ▁identified ▁in ▁ 1 9 9 5 , ▁several ▁th era pe ut ic ▁approaches ▁have ▁been ▁proposed ▁and ▁investig ated ▁that ▁primarily ▁focus ▁on ▁increasing ▁the ▁avail ability ▁of ▁SM N ▁protein ▁in ▁motor ▁neur ons . ▁The ▁main ▁research ▁directions ▁are ▁as ▁follows : ▁ ▁SM N 1 ▁gene ▁replacement ▁ ▁Gene ▁ther apy ▁in ▁S MA ▁a ims ▁at ▁rest oring ▁the ▁SM N 1 ▁gene ▁function ▁through ▁inserting ▁spe cially ▁craft ed ▁nucle ot ide ▁sequence ▁( a ▁SM N 1 ▁trans g ene ) ▁into ▁the ▁cell ▁nucle us ▁using ▁a ▁vir al ▁vector ; ▁sc AA V - 9 ▁and ▁sc AA V - 1 0 ▁are ▁the ▁primary ▁vir al ▁vectors ▁under ▁investigation . ▁ ▁In ▁ 2 0 1 9 ▁an ▁A AV 9 ▁ther apy ▁was ▁approved : ▁On as em n ogene ▁ab e par v ove c . ▁