IL6 and fibromyalgia: Indeed, Schwarz et al. [69] investigated altered tryptophan metabolism, along with the depletion of this amino acid, in n = 17 fibromyalgia patients; although these cases reacted similarly to an age-matched healthy control group for most markers evaluated, the fibromyalgia patient cohort had significantly elevated interleukin-6 (IL-6) concentrations.