FGF21 and obesity due to melanocortin 4 receptor deficiency: We matched a smaller group of 20 patients with both mut0 (low to no methylmalonyl-CoA enzymatic activity) and mut– (moderate methylmalonyl-CoA activity) MMA, 10 with very high FGF21 and 10 with lower values, with a subset of 20 sex-, age-, and BMI-matched control individuals recruited from an obesity study and performed a screen using the SomaScan platform, as previously described (52–54).