GPC4 and Parkinson disease: In serum, GPC-4 concentrations were about 10-times higher as compared to CSF, with a mean of 3371 ± 1078 [range 1696.1–5720.2] pg/ml in PD patients versus 3371 ± 1344 [range 1182.2–6920.7] pg/ml in CTR.