BDNF and Parkinson disease: Although the correlation between BDNF gene polymorphism and cognitive function has been observed in persons with normal ageing, neurodegenerative diseases (e.g., AD and PD), multiple sclerosis, and some mental disorders (Harrisberger et al., 2015; Shen et al., 2018; Cechova et al., 2020; Portaccio et al., 2021; Dolcetti et al., 2022), the evidence in patients with VaD (particularly SIVD) is limited.