Because extensive data from epidemiological studies have consistently confirmed that obesity, diabetes, and metabolic syndrome increase the risk of developing cognitive impairment and dementia (Baker et al., 2011; McCrimmon et al., 2012; Lehtisalo et al., 2016; Espeland et al., 2017; Pal et al., 2018), it is not surprising that more than 10 years ago, leptin was proposed to be the biochemical “link” connecting all of these pathologies (Harvey, 2010). The gene discussed is LEP; the disease is Cognitive impairment.