In this study, we utilized an αSyn-overexpressing human neuroglioma cell line (H4) and DA neurons generated from induced pluripotent stem cells (iPSC) of PD patients (SNCA triplication and A53T SNCA point mutation) to examine the trafficking, maturation and proteolytic activity of CTSD, CTSB, and CTSL as well as therapeutic mechanisms to rescue their enzymatic function. Here, CTSD is linked to Parkinson disease.