▁. ▁L ung ▁disease ▁is ▁inherited ▁in ▁an ▁aut os om al ▁re cess ive ▁manner , ▁requiring ▁mut ations ▁in ▁both ▁alle les . ▁Sur fact ant ▁produced ▁by ▁inf ants ▁with ▁SP - B ▁def ic iency ▁is ▁ab normal ▁in ▁composition ▁and ▁does ▁not ▁function ▁normally ▁in ▁lower ing ▁surface ▁t ension . ▁ ▁More ▁than ▁ 4 0 ▁different ▁mut ations ▁along ▁the ▁length ▁of ▁SF TP B ▁gene ▁have ▁been ▁account ed ▁for ▁in ▁sur fact ant ▁met abol ism ▁d ys function . ▁SF TP B ▁mut ations ▁are ▁inherited ▁in ▁aut os om al ▁re cess ive ▁fashion , ▁loss - of - function ▁mut ation ▁on ▁both ▁alle les ▁are ▁required ▁for ▁full ▁expression ▁of ▁disease . ▁About ▁ 2 / 3 ▁or ▁ 6 0 % - 7 0 % ▁of ▁those ▁account ed ▁disease - ca using ▁alle les ▁come ▁from ▁a ▁frames h ift ▁mut ation , ▁called ▁ 1 2 1 ins 2 , ▁on ▁ex on ▁ 4 ▁of ▁SF TP B ▁gene , ▁which ▁also ▁accounts ▁for ▁~ 6 5 % ▁of ▁US ▁cases . ▁The ▁rest ▁of ▁the ▁mut ated ▁alle les ▁come ▁from ▁n ons ense , ▁miss ense , ▁sp lice - site ▁mut ations , ▁and ▁other ▁possible ▁insert ion ▁and ▁delet ion ▁mut ations ▁throughout ▁the ▁entire ▁gene . ▁These ▁mut ations ▁cause ▁total ▁absence ▁or ▁loss - of - function ▁of ▁SP - B ▁and ▁lead ▁to ▁im bal ance ▁in ▁sur fact