Furthermore, they found that PD patients with unintended weight loss had lower leptin levels.12,13 Serum leptin concentrations correlate to body fat mass in PD patients with and without decreased weight and HCs.11,12 Moreover, Pelleymounter, et al revealed that leptin associates with body fat and weight loss by decreasing food intake and increasing energy expenditure.        24  These results express the hypothesis that the cause of leptin levels abnormality in PD patients maybe reduction of body fat mass. The gene discussed is LEP; the disease is Parkinson disease.