Molybdenum cofactor deficiency A (OMIM phenotype number 252150) is an AR condition due inactivating variants in MOCS1, resulting in disease onset in infancy with poor feeding, intractable seizures, severe psychomotor retardation, hypouricemia with hypouricosuria, increased sulfite production with urinary excretion of sulfite, and increased xanthine production with xanthinuria and xanthine NL (Zaki et al., 2016; Johannes et al., 2022). Here, MOCS1 is linked to xanthinuria.