▁partially ▁processed ▁pro SP - C ▁shows ▁significance ▁of ▁m ature ▁SP - B ▁in ▁bi ogen esis ▁and ▁processing ▁of ▁SP - C . ▁Abs ences ▁of ▁both ▁pro SP - B ▁and ▁SP - B ▁prote ins ▁are ▁observed ▁in ▁frames h ift ▁and ▁n ons ense ▁mut ations ▁of ▁SF TP B , ▁while ▁low ▁level ▁of ▁pro SP - B ▁is ▁detected ▁in ▁miss ense , ▁in - frame ▁delet ion of ▁insert ion ▁mut ations . ▁However , ▁these ▁mut ations ▁prevent ▁pro SP - B ▁from ▁fully ▁m ature ▁into ▁SP - B , ▁resulting ▁in ▁def ic iency ▁of ▁SP - B ▁and ▁sur fact ant . ▁ ▁SF TP C ▁mut ations ▁Famil ial ▁cases ▁of ▁SP - C ▁d ys function ▁ ▁are ▁inherited ▁in ▁an ▁aut os om al ▁dominant ▁pattern , ▁although ▁the ▁on set ▁and ▁sever ity ▁of ▁lung ▁disease ▁are ▁highly ▁variable , ▁even ▁within ▁the ▁same ▁family . ▁ ▁More ▁than ▁ 4 0 ▁distinct ▁mut ation ▁variations ▁in ▁SF TP C ▁gene ▁have ▁also ▁been ▁described ▁in ▁patients . ▁Wild - type ▁SP - C ▁prote ins ▁are ▁embedded ▁inside ▁the ▁ph osph ol ip id ▁bil ayer ▁of ▁ep ith el ial ▁type ▁II ▁cell ▁and ▁function ▁to ▁generate ▁and ▁maintain ▁mon ol ayer ▁of ▁sur fact ant ▁on ▁al ve olar ▁surface . ▁Ind ividual s ▁with ▁mut ated ▁SF TP C ▁gen es ▁tend ▁to ▁manifest ▁lung ▁dise ases ▁in ▁late ▁child hood ▁or ▁ad