Urinary Tryptophan–Kynurenine Pathway Profiling in Bulgarian Children with Autism Spectrum Disorder (ASD): Neopterin Co-Varies with Kynurenine and Quinolinic Acid

TL;DR

This study found that in children with autism in Bulgaria, certain urine chemicals linked to immune and brain function are connected, suggesting possible biological patterns in autism.

Contribution

The study identifies novel associations between neopterin and kynurenine pathway metabolites in a pediatric ASD cohort.

Findings

Neopterin levels in urine strongly correlate with quinolinic acid and kynurenine in children with ASD.

These associations remain significant even after adjusting for creatinine levels.

The findings suggest a potential link between immune activity and tryptophan metabolism in ASD.

Abstract

Background/Objectives: Autism spectrum disorder (ASD) is biologically heterogeneous, and immune-linked variation may be associated with differences in tryptophan–kynurenine pathway (KP) metabolism. Here, we report a targeted urinary profile of KP metabolites, NAD (nicotinamide adenine dinucleotide), and neopterin in a Bulgarian pediatric ASD cohort to describe within-cohort patterns and associations. Methods: Second-morning, acid-stabilized spot urine was collected from 73 children with ASD in Bulgaria (3–13 years; 57 males; 16 females). No contemporaneous neurotypical control group was enrolled; therefore, laboratory-provided reference limits are reported only as contextual benchmarks and are not interpreted as ASD-specific abnormalities. Tryptophan (TRP), kynurenine (KYN), kynurenic acid (KYNA), 3-hydroxykynurenine (3-HK), quinolinic acid (QUIN), NAD, and neopterin were quantified and derived indices were computed (KYN/TRP × 1000; QUIN/KYNA). Non-parametric statistics, Benjamini–Hochberg false discovery rate (FDR) correction, and Spearman correlation analyses were applied. Results: Neopterin was strongly associated with QUIN and KYN in creatinine-normalized data (QUIN: ρ = 0.59, q36 = 2.64 × 10−7; KYN: ρ = 0.54, q36 = 3.69 × 10−6); these associations persisted when reconstructed as absolute concentrations (e.g., QUIN_abs: ρ = 0.68, q36 = 2.69 × 10−10) and after partial Spearman correlation controlling for spot creatinine (partial ρ = 0.46, q = 2.52 × 10−4). One NAD value was <LOQ and was imputed as ½LOQ; sensitivity analyses did not materially change inference. Conclusions: In this ASD-only cross-sectional dataset, urinary neopterin levels co-varied with urinary KYN and QUIN and with KP indices. Clinical interpretation and causal inference require controlled and longitudinal studies with richer covariate capture.

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