They further found that 55 piRNAs that were differentially expressed in the amygdala of patients with PD were predicted to target 20 protein-coding genes, including Mitochondrially encoded cytochrome C oxidase I (MT-CO1) and MT-CO3 (Zhang and Wong, 2022), which encode the protein components of respiratory complex IV of the electron transport chain and are implicated in PD (Bartels and Leenders, 2010; Foti et al., 2019; Choong et al., 2021). This evidence concerns the gene MT-CO3 and Parkinson disease.