Molybdenum Cofactor Deficiency Type B Mimicking Hypoxic-Ischemic Encephalopathy in a Neonate: The First Genetically Confirmed Case in Korea

다국어 초록 (Multilingual Abstract)

Molybdenum cofactor deficiency (MoCD) is a rare autosomal recessive neurodegenerative disorder that often mimics hypoxic-ischemic encephalopathy (HIE) in neonates, leading to delayed diagnosis. Here, a term female neonate developed refractory seizures on day 3 of life with persistent hypouricemia. Magnetic resonance imaging revealed diffuse cortical and subcortical diffusion restriction, basal ganglia and thalamic involvement, white matter injury, and cerebellar hypoplasia, which were initially misinterpreted as HIE in the absence of a sentinel hypoxic-ischemic event. Serial neuroimaging showed rapidly progressive leukomalacia, and trio-based whole-genome sequencing ultimately identified a homozygous likely pathogenic variant in the MOCS2 gene, c.265T>C, p.*89Glnext*3. Both parents were confirmed as heterozygous carriers, establishing a diagnosis of MoCD type B and representing the first genetically confirmed case in South Korea. Despite aggressive anti-seizure therapy, dietary protein restriction, and supportive care, the patient exhibited severe global developmental delay and spasticity at 12 months of age, underscoring the poor prognosis of early-onset MoCD and the need to consider this entity in neonates with HIE-like encephalopathy, negative standard metabolic workup, and unexplained hypouricemia.