Calculation of M1 revealed a significant reduction in the proportion of NMNAT3 expressed in TH-positive DA neurones in PD SN (37 ± 6% versus 25 ± 7%, P = 0.037, n = 4 for each), whereas M2 revealed no change in the proportion of TH expressed in NMNAT3-positive neurones (65 ± 15% versus 47 ± 12%, P = 0.11, n = 4 for each), suggesting that those TH-positive DA neurones remaining still expressed NMNAT3. Here, TH is linked to Parkinson disease.