SAA2 and Parkinson disease: ELISA analysis (from 36 PD patients and 27 controls) of serum for SAA 1/2 protein expression, demonstrated decreased protein concentration levels in the serum of PD patients by 50.9% compared to controls (Figure 3, p = 0.0021), with the mean protein concentrations being 32.8 and 66.8 μg/ml, respectively.