PCP4 (also known as PEP‐19) in particular regulates Ca2+ binding to calmodulin, and the levels of transcript and protein of PEP‐19 are reduced in striatum of the MPTP mouse model of PD.41 In addition, we found higher expression of ATP13A4, cation‐transporting, P5‐type adenosine triphosphatase, among the ventral SNpc neurons. This evidence concerns the gene PCP4 and Parkinson disease.