Fig. 3.

Lower serum Trp levels accompany kynurenine-pathway activation. a, Cohort 2 overview: serum samples from 198 patients with CIDs plus 179 controls were selected for mass spectrometry-based targeted metabolomics. Additionally, 164 stool samples from patients with CIDs were sent for metabolomics analysis. Patients were selected for cohort 2 based on available HPLC-based Trp measurements (below 45 μM and above 60 μM). Mass spectrometry-based serum Trp measurements are included here as an overview. b, Faecal Trp levels in high and low serum Trp groups. c, Partial Spearman's correlations between Trp and the other measured proteogenic amino acids. Correlations with FDR <0.05 are circled in black, with increasing circle size denoting decreasing FDR via calculation of -log₁₀(FDR). d-i, Serum levels of selected Trp derivatives and the ratio of kynurenine-to-Trp (Kyn:Trp). Diamonds indicate means and comparisons are made against the control group. Significance annotation: ∗ FDR <0.05, ∗∗ FDR <0.01, ∗∗∗ FDR <0.001.