OAT (Ornithine Aminotransferase): OAT is a gene that encodes the ornithine aminotransferase enzyme, which plays a key role in the urea cycle. This enzyme catalyzes the conversion of ornithine to citrulline, helping the body detoxify ammonia. Mutations in OAT can disrupt this process, leading to hyperammonemia — a condition marked by elevated blood ammonia levels that can affect neurological function.