PRRT2 and Parkinson disease: Along the same line, we pose questionson whether this could provide further linkage between reports on cigarettesmoking (and thus elevated levels of CO 87) and the inverse association with cognitive function relateddisorders, such as Parkinson’s disease.88 Through proposing a possible dopamine/HO/CO axis, we hopeto stimulate investigations into this intriguing area of research.Although no direct links in regulating this axis have been reportedso far, two possible connections could be through protein kinase C(PKC) and neuronal hemoglobin (nHb).