One study found that transplanted fetal midbrain DA neurons survived without pathology after up to 14 years, suggesting the safety and feasibility of transplanted fetal brain cells for the treatment of PD [53], other two studies found that alpha-synuclein-positive lewy bodies eventually spread to the transplanted DA neurons in PD patients after 14 or 16 years of transplantation [54, 55]. Here, SNCA is linked to Parkinson disease.