Thus, it is also tempting to speculate that, while testosterone is neuroprotective in regions affected in AD, such as cortex and hippocampus, it is not protective, or is not efficiently converted into E2, in PD affected regions, such as the midbrain, which in turn could be due to different spatial expression of aromatase between the two diseases. The gene discussed is CYP19A1; the disease is Parkinson disease.