KLK4 and Alzheimer disease: Compared to the four plasma proteins in the CN group, the plasma level of KLK4, and GSN (4.27 ± 1.31 ng/ml, 33.87 ± 7.08 μg/ml, respectively, P < 0.001) were significantly increased, and the plasma level of sLRP1 and Caspase 3 (2.79 ± 0.98 μg/ml, and 6.30 ± 3.50 ng/ml, P < 0.01 or 0.001) were significantly decreased in the AD group.