They found decreased cytokine levels, such as neuropeptide Y [26], leptin [27], and brain-derived neurotrophic factor (BDNF) [22] in BD relative to UD, as well as increased levels of kynurenine, kynurenine/tryptophan ratio, and most interleukins (IL) [25]. This evidence concerns the gene BDNF and Behcet disease.