A growing body of epidemiological and molecular evidence now suggests an obvious relationship between brain insulin resistance, dementia due to Alzheimer's disease (AD), Parkinson's disease (PD), and AD/PD-related dementias (Bosco et al., 2012; de la Monte, 2012; Talbot, 2014; Athauda and Foltynie, 2016; Biessels and Despa, 2018; Ferreira et al., 2018; Hong et al., 2020). The gene discussed is INS; the disease is Parkinson disease.