SFXN5 (sideroflexin 5) is a mitochondrial transmembrane protein that functions as an amino acid and metabolite transporter, with specialized roles in metabolic regulation. The protein primarily transports citrate across mitochondrial membranes but does not transport serine 1. SFXN5 is predominantly expressed in the brain, with high expression levels detected across all analyzed brain regions 2. In brown adipose tissue, SFXN5 plays a regulatory role in UCP1-dependent thermogenesis, likely by supporting mitochondrial glycerol-3-phosphate utilization 3. The protein has been identified as a modulator of BAT thermogenesis and adiposity, with expression levels correlating with metabolic disease parameters 3. SFXN5 belongs to the evolutionary conserved sideroflexin family (SLC56), which exhibits functional specialization in mitochondrial metabolism and cellular homeostasis 1. Disease relevance includes potential involvement in medulloblastoma, where SFXN5 shows differential expression in certain tumor subtypes 4, and fatty liver disease, where it displays altered transcript usage patterns across species 5. The gene has also been studied as a candidate for Parkinson's disease, though mutations were not found to be pathogenic 2.