GCH1 and familial dilated cardiomyopathy: The DCM group had lower levels of GCH1 (71 ± 21 au versus 100 ± 22 au, P < 0.01; Fig. 3A) and higher levels of SPR (126 ± 23 au versus 100 ± 34 au, P < 0.05; Fig. 3B) than the CNT group.