The co-expression and co-regulation of ACE2 and DDC are corroborated by findings such as high ACE2 expression in dopaminergic neurons and its reduction in Parkinson’s disease (characterized by dopamine deficiency) [50], the increase in brain dopamine content following infusion of angiotensin 1–7 in the hypothalamus of rats [51], as well as dramatically low serotonin levels in the blood and the brain of ACE2-knockout mice [52]. Here, ACE2 is linked to Parkinson disease.