Increased prevalence of PD in diabetic patients. Insulin plays a vital role in the dopaminergic cells. There are shared pathways between insulin resistance and PD. Insulin treatment has a neuroprotective role in PD. Insulin could impact dopamine synthesis and clearance through its effect on tyrosine hydroxylase. Anti-diabetic drugs that treat insulin-resistant could have a protective function. The gene discussed is TH; the disease is Parkinson disease.