agn osis ▁ ▁The ▁most ▁severe ▁manifest ation ▁on ▁the ▁S MA ▁spectrum ▁can ▁be ▁notice able ▁to ▁moth ers ▁late ▁in ▁their ▁pre gn ancy ▁by ▁reduced ▁or ▁absent ▁f etal ▁movements . ▁Sym pt oms ▁are ▁critical ▁( including ▁resp ir atory ▁dist ress ▁and ▁poor ▁feed ing ) ▁which ▁usually ▁result ▁in ▁death ▁within ▁weeks , ▁in ▁contrast ▁to ▁the ▁m ild est ▁phen ot ype ▁of ▁S MA ▁( ad ult - ons et ), ▁where ▁mus cle ▁weak ness ▁may ▁present ▁after ▁dec ades ▁and ▁progress ▁to ▁the ▁use ▁of ▁a ▁wheel ch air ▁but ▁life ▁expect ancy ▁is ▁un changed . ▁ ▁The ▁more ▁common ▁clin ical ▁manifest ations ▁of ▁the ▁S MA ▁spectrum ▁that ▁prompt ▁di agnostic ▁gen etic ▁testing : ▁ ▁Progress ive ▁bil ater al ▁mus cle ▁weak ness ▁( Us ually ▁upper ▁arms ▁& ▁legs ▁more ▁so ▁than ▁hands ▁and ▁feet ) ▁preced ed ▁by ▁an ▁asympt om atic ▁period ▁( all ▁but ▁most ▁severe ▁type ▁ 0 ) ▁ ▁Fl atten ing ▁of ▁the ▁ch est ▁wall ▁when ▁taking ▁a ▁breath ▁and ▁bel ly ▁pro tr usion ▁when ▁taking ▁a ▁breath ▁in . ▁ ▁hyp ot onia   associ ated ▁with ▁absent   ref lex es . ▁While ▁the ▁above ▁sympt oms ▁point ▁towards ▁S MA , ▁the ▁diagn osis ▁can ▁only ▁be ▁confirmed ▁with ▁absolute ▁certain ty ▁through ▁gen etic ▁testing ▁for ▁bi - alle lic ▁delet ion ▁of ▁ex on ▁ 7 ▁of ▁the ▁SM N 1 ▁gene ▁which ▁is