▁in ▁ep ith el ial ▁type ▁II ▁cells ▁and ▁up - reg ulation ▁of ▁U PR . ▁SF TP C ▁mut ation ▁with ▁highest ▁occurrence ▁frequency ▁is ▁substitution ▁of ▁thre on ine ▁for ▁is ole uc ine ▁in ▁cod on ▁ 7 3 , ▁term ed ▁I 7 3 T , ▁found ▁in ▁more ▁than ▁ 2 5 % ▁of ▁patients ▁with ▁SP - C ▁related ▁dis orders . ▁St aining ▁of ▁pro SP - C ▁shows ▁diff use ▁st aining ▁strictly ▁in ▁cy top las m ▁and ▁accum ulation ▁of ▁imm un ore active ▁subst ances ▁surrounding ▁the ▁nucle us . ▁E valu ation ▁of ▁dise ases ▁related ▁to ▁SF TP C ▁mut ations ▁show ▁association ▁with ▁chron ic ▁par en ch ym al ▁lung ▁disease . ▁ ▁ABC A 3 ▁mut ations ▁ ▁Mut ations ▁in ▁ABC A 3 ▁appear ▁to ▁be ▁the ▁most ▁common ▁cause ▁of ▁gen etic ▁sur fact ant ▁d ys function ▁in ▁humans . ▁The ▁mut ations ▁result ▁in ▁a ▁loss ▁of ▁or ▁reduced ▁function ▁of ▁the ▁ABC A 3 ▁protein , ▁and ▁are ▁inherited ▁in ▁an ▁aut os om al ▁re cess ive ▁manner ▁. ▁ ▁There ▁are ▁more ▁than ▁ 1 5 0 ▁different ▁mut ations ▁throughout ▁ABC A 3 ▁gene ▁with ▁various ▁alle lic ▁heter ogene ity , ▁making ▁it ▁the ▁biggest ▁class ▁of ▁gen etic ▁cause ▁of ▁sur fact ant ▁d ys function . Like ▁SP - B ▁def ic iency , ▁ABC A 3 ▁mut ations ▁are ▁inherited ▁in ▁aut os om