( ( If untreated ) ( , ( they ( often ( ( ( die ( of ( heart ( ( attack or ) stroke ) ) ) ) ( before ( reaching adulthood ) ) ) . ) ) ) ) )
(ROOT (S (SBAR (IN If) (FRAG (ADJP (JJ untreated)))) (, ,) (NP (PRP they)) (ADVP (RB often)) (VP (VBP die) (PP (IN of) (NP (NN heart) (NN attack) (CC or) (NN stroke))) (PP (IN before) (S (VP (VBG reaching) (NP (NN adulthood)))))) (. .)))
If untreated, they often die of heart attack or stroke before reaching adulthood.
(ROOT (S (NP (DT A) (NN heart) (NN attack) (CC or) (NN stroke)) (VP (VBZ is) (ADVP (RB often)) (NP (NP (DT a) (NN result)) (PP (IN of) (NP (JJ untreated) (NNS atherosclerosis))))) (. .)))