Molybdenum Cofactor Deficiency (MOCOD) is a rare often fatal autosomal recessive disorder. We report a case of genetically confirmed MOCOD in an infant presenting with refractory neonatal seizures, with a family history of Dandy-Walker malformation (DWM). A term baby girl was the second born to consanguineous parents. Her elder sister had spasticity, developmental delay, seizures, and DWM, passed away at 8-years-old. On day two of life, the baby developed respiratory distress, recurrent apneic attacks, poor sucking, feeding difficulties, and refractory generalized tonic-clonic convulsions. CT brain revealed global cerebral ischemia, and EEG was normal. Biochemical tests showed hypouricaemic hypouricosuria with a serum uric acid level of 17 µmol/L (119-327), and uric acid to creatinine ratio (spot urine sample) of 0.1 µmol:µmol (0.7-1.5). In the presence of neurological manifestations, hypouricaemic hypouricosuria, potentially indicative of MOCOD. Further analysis revealed increased plasma xanthine 70 µmol/L and hypoxanthine 542 µmol/L with elevated urine xanthine 0.202 mmol/L (0.01-0.09), though urine S-sulphocysteine levels were normal 2 µm/mM (0-10). Unfortunately, the baby’s condition deteriorated further, and passed away on day 15 of life. All exons and flanking intronic regions of the MOCS1 and MOCS2 were amplified and analyzed by PCR-Sanger sequencing from genomic DNA. The patient was homozygous for a novel variant MOCS1 c.1807G>C, p.(Ala598Pro) in exon 10 which was consistent with the MOCOD phenotype which has not been reported in the literature.This case underscores the importance of early biochemical and genetic testing for MOCOD.Uric acid screening is a cost-effective tool for identifying neonates at risk for MOCOD.MOCOD type A is now treatable, starting Cyclic pyranopterin monophosphate (cPMP) substitution early yields rapid and sustained biochemical improvement, enhancing neurodevelopmental outcomes.

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