The serum transferrin (TRF, p < 0.0024) concentration and total iron binding capacity (TIBC, p < 0.0024) were lower in the apathetic group after Bonferroni correction, and they were negatively associated with AS scores in male participants with PD (TRF, r = −0.27, p = 0.010; TIBC, r = −0.259, p = 0.014). The gene discussed is TF; the disease is Parkinson disease.