Thus, the aims of the present study are: (1) to investigate the prevalence and associated risk factors of MCI in thalassemia patients, (2) to evaluate the clinical significance of FGF21 and associative risk factors of MCI in thalassemia patients, and (3) to investigate the mechanisms associated with FGF21 and iron-induced brain toxicity in thalassemic mice. The gene discussed is FGF21; the disease is thalassemia.