TH and Parkinson disease: Formaldehyde, a common cause of PD, reduces the expression of tyrosine hydroxylase, a key enzyme in DA synthesis, and induces PD-like neuronal damage.[54] In addition, formaldehyde increases intracellular iron concentration and upregulates ferroptosis-related genes, such as prostaglandin-endoperoxide synthase 2, glutaminase 2, SLC1A5, and SLC38A1 to induce ferroptosis in hippocampal neurons.[55] This suggests that formaldehyde may play a key role in ferroptosis in PD.