GPX4 volume density is increased from 0.0018 ± 0.0002 in controls (n = 11) to 0.0038 ± 0.0007 in PD (n = 12) (P = 0.0192), indicating that GPX4 is either upregulated in surviving neurons or that a greater percentage of cells not expressing GPX4 are lost compared to cells with GPX4. This evidence concerns the gene GPX4 and Parkinson disease.