While cathepsin K has the potential to ameliorate α-synuclein pathology by degrading α-synuclein amyloids,64 increased expression of the CTSS gene—together with other genes involved in the antigen processing and presentation pathway and related immune pathways such as HLA-DQA1, HLA-DRA, HLA-DPA1,and HLA-DMB—was reported in idiopathic PD patients in a study in which brain transcriptomic profiling was performed in idiopathic and LRRK2-associated PD.65 This evidence concerns the gene LRRK2 and Parkinson disease.