DDC and COVID-19: Based on the genetic co-expression of ACE2 and dopa-decarboxylase (DDC, the enzyme converting dihydroxyphenylalanine into dopamine and hydroxytryptophan into serotonin), one can assume that a dysfunctional collaboration between ACE2-mediated synthesis of angiotensin 1-7 and disrupted dopamine synthesis might incriminate COVID-19 in triggering PD neurodegenerative mechanisms [33,38].