DKKL1 and Parkinson disease: Although the expression of DKKL1 is necessary for normal nerve development, the over-expression of DKKL1 is the characteristic of many neurodegenerative diseases, such as stroke, Alzheimer's disease, Parkinson's disease, and temporal lobe epilepsy (27), and it can play an important role in pathological conditions such as tumorigenesis and cancer progression (28).