Specific proteins, e.g., α-synuclein (α-syn) [15,16,17,18,19] and clusterin [20] in Parkinson ́s disease (PD); creatinine, human serum albumin (HSA), and TAR DNA binding protein 43 kDa (TDP-43) in amyotrophic lateral sclerosis (ALS) [21,22,23]; as well as RNAs’ biomarkers [24] have been discovered in biofluids. The gene discussed is CLU; the disease is Parkinson disease.