FGF21 and thalassemia: Major findings from this study are as follows: (1) MCI condition occurred in thalassemia patients, (2) hematologic parameters including serum ferritin level and maximum level of serum ferritin in the past 5 years were significantly increased in thalassemia patients with MCI, (3) clinically, plasma FGF21 level showed an independent association with MCI, (4) mechanistically, brain FGF21 resistance may be related to the alteration of brain synaptic protein and Alzheimer’s like pathology, and (5) MCI in thalassemia patients may be associated with FGF21 resistance.