Although still controversial with respect to the intracellular type, KLK6 inefficiency in α-synuclein degradation seems to contribute to PD pathogenesis, probably due to an altered trafficking of KLK6 [187, 190] or to the resistance of certain forms of α-synuclein to KLK6-proteolysis [76, 191]. This evidence concerns the gene KLK6 and Parkinson disease.