Early Neonatal Fosdenopterin Treatment for Molybdenum Cofactor Deficiency Type A: New Insights into Its Natural History and Potential Role for Fetal Therapy.

Introduction: Molybdenum cofactor deficiency (MoCD) is a rare, lethal disorder characterized by early-onset encephalopathy and seizures. In 2021, fosdenopterin (NulibryTM) became the first FDA-approved treatment for MoCD type A (MoCD-A). Case Presentation: A G3P2 woman with a prior affected child underwent prenatal diagnosis of MoCD-A at 16 weeks via amniocentesis. Fetal Magnetic Resonance Imaging (MRI) at 22 weeks was normal but showed a mega cisterna magna by 28 weeks. Concerns of ongoing brain damage led to a cesarean section at 32 weeks 6 days estimated gestational age (EGA). Intravenous fosdenopterin was administered within 10 min of birth. Seizures started around 12 h and escalated to status epilepticus by 24 h but resolved by 60 h with treatment. Early MRI demonstrated acute injury without chronic changes. The infant was discharged on day 37 and diagnosed with spastic quadriplegic cerebral palsy at 6 months, with cognition relatively spared. At 24 months, the child remains seizure-free with moderate motor impairment. Conclusions: This case highlights that brain injury in MoCD-A may commence in utero during the second trimester. Early delivery combined with immediate neonatal fosdenopterin treatment controlled seizures and halted progression, but residual injury suggests that prenatal interventions are necessary to optimize outcomes.