Interdonor heterogeneity in kynurenine levels is partly explained by genetic regulation. Kynurenine measurements in identical monozygotic twins vs nonidentical dizygotic twins (A) shows potential heritability of kynurenine levels, with stronger twin-twin correlations in the former than in the latter group (B-C). (D) mQTL analysis was performed to determine the genetic polymorphisms associated with interdonor heterogeneity in the end-of-storage kynurenine levels in the REDS RBC Omics index donor cohort (n = 13 091). (E) The 3D uMAP overlaps homozygous state for the dominant vs recessive SNP (SLC7A5, rs8052118, and intronic) associated with significant elevation in RBC kynurenine levels. (F) Volcano plot shows log2 fold-changes between the 2 groups. (G-H) Volcano plot of the Spearman association of metabolite levels to the dosage of the most significant SNP associated with kynurenine levels. (I) The lowest kynurenine levels were observed in donors who were homozygous dominant for SLC7A5 and recessive for ATXN2. FA, fatty acid; HD, homozygous dominant; HR, homozygous recessive; KMO, kynurenine monooxygenase; TDO, tryptophan dioxygenase.