Given that pyridoxal 5’-phosphate (PLP), a biologically active form of vitamin B6 (hereinafter defined as Vit-B6), is a well-known cofactor of the key enzymes (including Kyn aminotransferases and kynureninase) for Kyn catabolism13, we first checked PLP concentrations using aforementioned serum samples collected from subjects that were overweight or affected by obesity. This evidence concerns the gene KYNU and obesity due to melanocortin 4 receptor deficiency.