RTN4R and obesity due to melanocortin 4 receptor deficiency: These unadjusted associations identified species that have been associated with insulin resistance and obesity for the protein (eg, CES1, INHBC, RTN4R) [30, 31], metabolite (α-aminoadipate, butyryl carnitine, tyrosine) [32, 33], and lipid (TG and DG species) assays [34].