A Monoallelic DNM1L Mutation presenting with Epilepsia Partialis Continua: A Case Report

Background: Variants in DNM1L are reported as a rare cause of refractory epilepsy and status epilepticus. We report a patient with epilepsia partialis continua (EPC) secondary to a monoallelic DNM1L mutation. Case Information: An 11-year-old boy with prior history of speech delay and well-controlled absence epilepsy on valproate presented in clinic with status epilepticus and posterior frontal diffusion restriction on MRI. Seizures were characterized by hemifacial clonus consistent with EPC. Extensive workup including EEG, MRI, cytokine, and encephalitis panels were unrevealing for etiology. Genetic peroxisomal panel revealed a monoallelic missense mutation (R403C) in the DNM1L locus as cause for his EPC. GDF15 was also elevated, reaffirming the presence of mitochondrial disease. This DNM1L mutation was determined to be the underlying etiology for his presentation. Lacosamide, clobazam and phenobarbital, among other interventions, were ultimately used to control the patient's epilepsy; he was sent home after extensive stays in the PICU and inpatient rehabilitation unit. Conclusions: DNM1L mutations can cause cerebral dysmyelinations, abnormal gyral patterns, microcephaly, and death within the first year of life. Yet several recent cases, including ours, have linked DNM1L variants with other neurological phenotypes, including a late onset of symptoms such as intractable epilepsy, myoclonus, and developmental delay. This case is strikingly like that of a previous report but with additional clinical features such as aphasia and EPC. The presentation of EPC in our patient, as well as the difficulty finding its etiology, exemplifies the unclear clinical pattern that remains with DNM1L mutations. The clinical ambiguity of this mutation complicates diagnosis and demonstrates the importance of prompt genetic testing.