Some studies have found Tf concentrations in the circulation (Logroscino et al. 1997) and brain tissue (substantia nigra (Ayton et al. 2016) and temporal cortices (Sabbir 2024)) to be significantly lower in PD patients compared to the CG, while Xu et al. (2018) found increased Tf levels in the serum of PD patients (Xu et al. 2018). This evidence concerns the gene TF and Parkinson disease.