Genetic underpinnings of RBC carnitine levels in JAX Diversity Outbred mice. Eight genetically diverse founder strains underwent crossbreeding for 6 generations to obtain 350 genetically diverse mice. AC levels were measured at baseline and upon refrigerated storage of RBCs from these mice for 7 days (equivalent to day 42 in humans; A). (B) No significant false discovery rate–corrected association was observed between carnitine levels and genotypes, as gleaned by >120 000 SNPs monitored in this study. (C) However, mQTL analyses for end-of-storage carnitine showed an association with polymorphisms in a region on chromosome 11, (D) coding for the SLC22A5 transporter. (E) These associations held true for almost all the ACs tested here. (F) At the end of storage, RBCs from the 350 mice were transfused into ubi-GFP⁺ recipient mice to determine the correlations between end-of-storage AC pools and the percentage of transfused RBCs that still circulate upon 24h from transfusion. (G) Strong negative associations were observed for a series of hydroxy-ACs and other short/odd-chain ACs (eg, 3:0 and 9:0; representative scatter plots in panel G derived from the breakdown of oxidized fatty acids.