▁are ▁not ▁apparent ▁until ▁ad ul th ood . ▁All ▁generally ▁result ▁in ▁w ors ening ▁mus cle ▁weak ness ▁associated ▁with ▁mus cle ▁tw itch ing . ▁Arm , ▁leg ▁and ▁resp ir atory ▁mus cles ▁are ▁generally ▁affected ▁first . ▁Associ ated ▁problems ▁may ▁include ▁problems ▁with ▁sw allow ing , ▁sc ol ios is , ▁and ▁joint ▁contract ures . ▁S MA ▁is ▁a ▁leading ▁gen etic ▁cause ▁of ▁death ▁in ▁inf ants . ▁ ▁Sp inal ▁mus cular ▁at ro phy ▁is ▁due ▁to ▁a ▁gen etic ▁defect ▁in ▁the ▁SM N 1 ▁gene . ▁They ▁are ▁inherited ▁from ▁a ▁person ' s ▁parents ▁in ▁an ▁aut os om al ▁re cess ive ▁manner . ▁The ▁SM N 1 ▁gene ▁enc odes ▁SM N , ▁a ▁protein ▁necessary ▁for ▁surv ival ▁of ▁motor ▁neur ons . ▁L oss ▁of ▁these ▁neur ons ▁prevents ▁the ▁sending ▁of ▁signals ▁between ▁the ▁brain ▁and ▁ske let al ▁mus cles . ▁Di agn osis ▁is ▁sus pected ▁based ▁on ▁sympt oms ▁and ▁confirmed ▁by ▁gen etic ▁testing . ▁ ▁Tre at ments ▁include ▁support ive ▁care ▁such ▁as ▁physical ▁ther apy , ▁nut r ition ▁support , ▁and ▁mechanical ▁vent ilation . ▁The ▁medic ation ▁n us in ers en , ▁which ▁is ▁inject ed ▁around ▁the ▁sp inal ▁cord , ▁slow s ▁the ▁pro gression ▁of ▁the ▁disease ▁and ▁impro ves ▁mus cle ▁function . ▁In ▁ 2 0 1 9 , ▁the ▁gene ▁ther apy ▁on as em n ogene ▁ab