Refractory Seizures and Encephalopathy in a Neonate: A Rare Case of Molybdenum Cofactor Deficiency Type B - A Case Report

Background: Molybdenum cofactor deficiency (MoCD) is a rare autosomal recessive inborn error of metabolism causing deficiency in molybdenum-dependent enzymes, leading to accumulation of toxic metabolites such as sulfite, resulting in severe neurological damage. We describe a neonate with MoCD type B. Clinical Description: A term neonate, the third child of third-degree consanguineous parents, presented with seizures and encephalopathy shortly after birth. There were two prior sibling deaths due to neonatal seizures. The neonate had hypotonia and exaggerated startle response (hyperekplexia) but no facial dysmorphism. Management and Outcome: Biochemical testing showed undetectable serum uric acid. Brain magnetic resonance imaging revealed findings classical of MoCD with cystic encephalomalacia and lactate peaks on magnetic resonance spectroscopy. Whole-exome sequencing confirmed a homozygous pathogenic variant in the MOCS2 gene. Conclusion: In neonates presenting with refractory seizures and encephalopathy soon after birth, without perinatal asphyxia, MoCD should be suspected, especially in the context of consanguinity or sibling deaths. Low uric acid and suggestive neuroimaging, guide the diagnosis, confirmed by genetic testing. Treatment remains supportive.