Abstract Details

Title SCN1A-associated Episodic Encephalopathy in a School-aged Child: A Phenotypic Overlap with Familial Hemiplegic Migraine?

Topic Epilepsy/Clinical Neurophysiology (EEG)

Presentation(s) P10 - Poster Session 10 (8:00 AM-9:00 AM)

Poster/Presentation
Number 10-009

Objective NA

Background Pathogenic variants in SCN1A are classically linked to epileptic encephalopathies such as Dravet syndrome and GEFS+, but have also been associated with familial hemiplegic migraine type 3 (FHM3). Recent studies indicate that certain SCN1A variants may produce mixed phenotypes, blurring clinical boundaries between epilepsy, migraine, and episodic encephalopathy, thereby complicating diagnostic and therapeutic decisions.

Design/Methods NA

Results A 13-year-old right-handed male with a history of language delay, ADHD, and depression presented with recurrent episodes of altered awareness and abnormal behavior beginning at age 8. Episodes were triggered by exertion or illness and featured a prodrome of headache and dizziness, followed by pallor, unresponsiveness, glazed expression, toe-walking, nausea, and dream-like awareness. Events lasted 5–40 minutes, with prolonged postictal confusion. EEG showed rare generalized spike-wave discharges during sleep. Brain MRI and metabolic studies were unremarkable. Genetic testing identified a heterozygous pathogenic SCN1A variant (c.5620C>T; p.Arg1874Trp), inherited from an asymptomatic father. Symptoms resolved with Levetiracetam (750 mg BID), with no recurrence over 3 years. The absence of febrile seizures, hemiplegia, and developmental regression argued against classic epileptic encephalopathy. Given the episodic nature and associated symptoms, FHM3 remains a diagnostic consideration.

Conclusions This case illustrates the expanding phenotypic spectrum of SCN1A-related disorders and raises the possibility that FHM3 may present in childhood with atypical features mimicking epilepsy or encephalopathy. Functional studies and long-term phenotyping of individuals with SCN1A variants are needed to clarify genotype–phenotype correlations. Clinicians should consider FHM3 in exertion- or illness-induced episodic encephalopathy, particularly when associated with preserved cognition and a positive family history.

Authors/Disclosures
Lin Yao, MD, PhD (Texas Children's Hospital Baylor Medical School) PRESENTER	Dr. Yao has nothing to disclose.
Jeffrey Kuerbitz, PhD (Baylor Child Neurology)	Dr. Kuerbitz has nothing to disclose.
Melissa Mizerik, DO	Dr. Mizerik has nothing to disclose.
Maria Gonzalez, MD	Dr. Gonzalez has nothing to disclose.
Prescott Cheong, MD	Dr. Cheong has nothing to disclose.
Rachael Cheek	Dr. Cheek has nothing to disclose.
Jimmy Holder, MD (BCM)	Dr. Holder has received personal compensation in the range of $0-$499 for serving as a Consultant with Stoke Pharmaceutical.
Gary D. Clark, MD (Baylor College of Medicine)	The institution of Dr. Clark has received research support from Greewich pharmaceuticals. The institution of Dr. Clark has received research support from Novartis.
Mariam Hull, MD (Texas Children's Hospital, Pediatric Neurology)	Dr. Hull has received publishing royalties from a publication relating to health care.

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