DAT‐ir axon length density in R does not correlate with the number of TH+ neurons,14, 15 but does parallel the severity of parkinsonism: the more severe the condition, the higher the DAT‐ir axonal density in the R nucleus (Figs. 2, 3, 4F,I, 5D). The gene discussed is SLC6A3; the disease is Parkinson disease.