T3 not only controls the splicing of the AβPP gene but also regulates the processing and secretion of AβPP.31 A growing body of research has established the connection between learning and memory impairment, the onset of AD, and variations in TH levels and hypo- or hyperthyroidism.30 Similar effects on AD have been suggested for both hypo- and hyperthyroidism (Figure 3). Here, APP is linked to Alzheimer disease.