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Treatment and Management: Identification of the de novo FGF12 variant informed the same-day refinement of his lacosamide therapy, resulting in improved seizure control after multiple prior treatment failures.The molecular diagnosis also guided genetic counseling regarding prognosis and recurrence risk, including discussion of genotype-phenotype correlations and the increased risk of gonadal mosaicism.Outcome and Follow-Up: He was discharged after a 2-week initial hospitalization.Two months following discharge, he experienced four breakthrough seizures lasting 1-2 minutes each, and oxcarbazepine was added to his regimen.Since the initiation of oxcarbazepine, he has not had any known seizures.At present, his medications include levetiracetam, oxcarbazepine, lacosamide, and pantoprazole.At 5 months of age, he is beginning to show mild developmental delays but continues to make progress.Discussion: This variant is one of two recurrent pathogenic FGF12 variants and is associated with a more severe phenotype, consistent with this patient's early and refractory seizures.A detailed review and comparison of previously reported DEE47 cases is also presented.This case expands the phenotypic spectrum of DEE47, particularly the possibility of respiratory complications, and further demonstrates the potential for urGS to rapidly identify actionable molecular diagnoses in critically ill infants.Conclusion: This case expands the phenotypic spectrum of DEE47, particularly the possibility of respiratory complications, and highlights the utility of ultrarapid genome sequencing in guiding timely diagnosis and precision treatments in epilepsy.Introduction: Developmental and epileptic encephalopathies (DEEs) represent a genetically and phenotypically heterogeneous group of disorders characterized by seizures resistant to anti-epileptic drugs (AEDs) and developmental slowing or regression.Fibroblast growth factor 12 (FGF12) is a cytoplasmic protein that interacts with neuronal sodium channels and is critical for regulating neuronal excitability by delaying the fast inactivation of these channels.Pathogenic variants in FGF12 disrupt its regulation of sodium channels, leading to neuronal hyperexcitability and manifesting clinically as severe early-life epilepsy, or DEE47 (OMIM 617166).DEE47 is rare, with fewer than 30 cases reported to date.Case Presentation: We describe a male patient who presented on day of life (DOL) 44 with hypoxemia and hemoptysis.Imaging revealed bilateral pneumothoraces, and he was evaluated to determine the source of bleeding (pulmonary vs gastrointestinal).On DOL 47, he developed brief focal seizures, which progressed to breakthrough seizures and eventually refractory status epilepticus.Diagnostic Workup: Despite treatment with levetiracetam, phenobarbital, midazolam, and a medically induced coma with ketamine, his seizures persisted.Genetics was consulted on DOL 49 and ordered trio ultra-rapid genome sequencing (urGS).On DOL 52, ketamine was weaned and video EEG was replaced.His seizures persisted despite ongoing phenobarbital and maximum-dose levetiracetam, prompting the addition of lacosamide.Later that day, urGS resulted, revealing a de novo FGF12 [NM_021032.4]c.341G>A (p.Arg114His) pathogenic variant and establishing the molecular diagnosis of DEE47.This variant is one of two recurrent pathogenic FGF12 variants and is associated with a more severe phenotype than the recurrent c.334G>A (p.Gly112Ser) variant.