SLC25A45 is a mitochondrial inner membrane transporter that mediates the import of methylated amino acids into mitochondria, playing a crucial role in carnitine biosynthesis 12. The protein specifically transports methylated basic amino acids including asymmetric dimethylarginine (ADMA) and trimethyllysine (TML), but shows no affinity for unmethylated arginine and lysine 2. Mechanistically, SLC25A45 facilitates mitochondrial TML import, which serves as a precursor for carnitine synthesis, thereby connecting protein catabolism to carnitine production and sustaining β-oxidation during fasting conditions 1. The transporter is essential for maintaining mitochondrial protein synthesis, biogenesis of the oxidative phosphorylation system, and mitochondrial morphology 3. Disease relevance includes associations with cardiovascular function, as a non-synonymous mutation (R285C) associates with altered plasma methylated amino acid levels and lower resting heart rate 4. Additionally, rare variants in SLC25A45 have been linked to serum creatinine levels and chr11 kidney disease 5, and genomic variations show associations with preterm birth risk 6. The protein may also regulate mitochondrial NMN levels, affecting local NMN/NAD+ ratios 7.