TNF and Leigh syndrome: Previous work in both pediatric and adult LS has identified several cytokines across the T helper (Th)1, Th2, Th17, and macrophage activation-associated pathways, which are elevated in the peripheral blood of LS patients, including Interleukin (IL)-1, IL-2, IL-4, IL-8, IL-13, IL-33, Interferon-Gamma-Inducible Protein (IP-10 (also termed CXCL 10)), and Tumor Necrosis Factor (TNF)-α [10,11,12,13,14,15,16,17].