Weight loss occurs several years before diagnosis and is correlated with the severity and stage of diseases (Saute et al., 2012; Soto et al., 2012). Olfactory dysfunction is a clinical symptom of PD as well as a side effect of acetylcholinesterase inhibitors and dopaminergic drugs. It usually occurs early in the course of neurodegenerative diseases and results in inappetence eventually (Seo et al., 2018). Higher energy expenditure in PD, HD, and MJD results from dyskinesia and dystonia. Both increased energy consumption and reduced calorie intake may contribute to weight loss. NPY plays a vital role in the regulation of body weight and physiological control of food intake (Zhang et al., 2019). It is believed that NPY can be a potential therapeutic target in neurodegenerative diseases. The related mechanisms of NPY in neurodegenerative disease are summarized in Figure 1.