Supplementary Material for: Unraveling Alternating Hemiplegia of Childhood: A Case Report with Genetic and Clinical Insights

Introduction: Alternating Hemiplegia of Childhood (AHC) is a complex neurological disorder comprising paroxysmal episodes of repeated, transient paresis involving either or both sides of the body, with onset usually before the age of 18 months. The etiology is varied and includes channelopathy, mutations of ATP1A3 gene that encode alpha subunit of NA+-K+ ATPase pump.
Case presentation: A 7-month-old girl presented with tonic neck deviation of the neck and eyes, episodic hemiparesis affecting both sides alternatively. Each episode resolved after sleep and was precipitated by hunger, fever, and sleep deprivation. Neurological examination and lab workup, including MRI and EEG, were normal. Whole-exome sequencing revealed a heterozygous de novo pathogenic mutation in the ATP1A3 gene (p.Asp801Asn), confirming Alternating Hemiplegia of Childhood. She was started on flunarizine, a calcium-channel blocker. Significant clinical improvement and catch-up in developmental milestones were observed on follow-up.
Conclusion: AHC is frequently misdiagnosed due to its rarity and varied presentation. Diagnosis is clinical and supported by genetic testing. Mutations in ATP1A3 are common and often cluster at specific hotspots. Management includes symptomatic treatment and supportive care, with flunarizine offering some benefit. This case highlights the need for early recognition and genetic confirmation of AHC to initiate therapy and improve quality of life.