SUOX (sulfite oxidase) catalyzes the oxidation of sulfite to sulfate, the terminal reaction in oxidative degradation of sulfur-containing amino acids 1. This mitochondrial enzyme contains molybdopterin and heme cofactors and localizes to the mitochondrial matrix and inner membrane [GO annotations]. SUOX functions as part of the sulfide oxidation unit (SOU), playing a critical role in hydrogen sulfide metabolism and mitochondrial energy production through ATP synthesis via oxidative phosphorylation 23. Isolated sulfite oxidase deficiency (ISOD), caused by biallelic SUOX mutations, is a life-threatening autosomal recessive neurological disease with onset typically within the first 72 hours of life 1. Clinical features include seizures (84%), developmental delay (97%), hypotonia/hypertonia, feeding difficulties, and ectopia lentis, with brain abnormalities on imaging in all affected patients 14. Patients with missense mutations show milder symptoms and later disease onset compared to truncating mutations 4. Beyond monogenic disease, SUOX emerges as a prognostic biomarker in malignancies. Low SUOX expression correlates with poor prognosis in intrahepatic cholangiocarcinoma and pancreatic ductal adenocarcinoma 53. Additionally, SUOX variants are associated with susceptibility to gastroesophageal reflux disease and asthma 6, and polycystic ovary syndrome 7, suggesting broader metabolic roles.