SLC25A36 encodes a mitochondrial pyrimidine nucleotide transporter that mediates bidirectional transport of pyrimidine and guanine nucleotides across the inner mitochondrial membrane 1. The protein catalyzes antiport of cytosine, uracil, and guanine nucleotides (in deoxy and non-deoxy forms) at higher rates, with lower-rate uniport activity also documented 1. By exchanging intramitochondrial nucleotide mono- and diphosphates for cytosolic triphosphates, SLC25A36 supplies precursors essential for mitochondrial DNA and RNA synthesis while removing catabolic products 1. This nucleotide transport function is critical for mitochondrial genome maintenance and respiration regulation. Biallelic SLC25A36 mutations cause hyperinsulinism/hyperammonemia (HI/HA) syndrome, a severe metabolic disorder 23. Loss-of-function mutations reduce mitochondrial GTP content, leading to hyperactivation of glutamate dehydrogenase and excessive insulin secretion 2. Clinical manifestations include hyperinsulinism, hyperammonemia, seizures, hypothyroidism, and developmental delay 34. Emerging evidence suggests oral uridine supplementation may improve metabolic parameters and growth outcomes in affected patients 4. SLC25A36 was additionally identified among eight mitochondrial genes associated with calcific aortic valve disease pathogenesis 5, implicating nucleotide transport in valve disease mechanisms.