C3 and Parkinson disease: Male PD patients had lower levels of C3 and C4 than healthy controls [0.87 (0.22) vs. 0.96 (0.19); 0.19 (0.06) vs. 0.22 (0.07), respectively, Pc < 0.01] and lower levels of C3 than female PD patients [0.87 (0.22) vs. 1.02 (0.23), Pc < 0.01].