High plasma contents of the leptin hormone are known to be a frequent companion of obesity and a sign of metabolic disorders in individuals with obesity [12], which was confirmed in our study; the plasma leptin level was increased in obese patients with and without type 2 diabetes and positively correlated with the levels of proinflammatory cytokines (TNF-a, IL-6 and IL-8), glucose and vCAM-1, that indicate a negative role of the increase in the number of mtDNA in carbohydrate and lipid metabolism. This evidence concerns the gene LEP and type 2 diabetes mellitus.