MKI67 and Parkinson disease: The number of actively dividing NSCs (Ki67-positive) decreased more rapidly in PD-NSCs than WT-NSCs (3.8 folds vs 2.2 folds, Fig. 1k, l), which was accompanied by far more DSB DNA damage (γH2AX-positive foci) accumulation in PD-NSCs (Fig. 1m, n).