Patients with MMA, despite massive elevations in plasma mitochondrial markers, FGF21, and GDF15 concentrations (Supplemental Figure 6A), had overall lower inflammatory cytokine levels, including adipokines typically elevated in obesity and the metabolic syndrome (IFN-γ, TNF, IL-6, IL-12, IL-1B) (55, 56) compared with the age-, sex-, and BMI-matched control subset (Supplemental Figure 6, C and D, and Supplemental Table 2). Here, FGF21 is linked to obesity due to melanocortin 4 receptor deficiency.