Objective: To report an atypical case of alternating hemiplegia of childhood (AHC), which has not yet been reported in Korea.

Background: The ATP1A3 gene pathologic variant is detected in other distinct clinical syndromes, such as rapid-onset dystonia parkinsonism (RDP) and CAPOS syndrome (cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss). After the introduction of next-generation sequencing, intermediate cases and atypical cases, such as severe infantile epilepsy, severe hypotonia, relapsing encephalopathy and cerebellar ataxia, fever-induced weakness and encephalopathy, and rapid onset ataxia, have expanded the clinical spectrum of ATP1A3-related disorders.

Method: This is a case report.

Results: A 33-year-old man was admitted to our hospital with recurrent dyskinesia episodes. He had not had any problems during the perinatal period, but after his first birthday, his limbs had twisted intermittently. Symptoms occurred on either the right or left side limbs, starting from the leg to the arm, and occasionally occurred in the arm and leg simultaneously, or were only experienced on the arm or leg. When the attacks were not present, he could live normally and did not have cognitive dysfunction. The family history revealed that his cousin was diagnosed with cerebral palsy and died in her twenties.
 An initial neurological examination revealed motor weakness and dystonia on the right side and peripheral type facial palsy. There was no hearing loss or ataxic features, and other examination findings were normal. His mini-mental status exam score was 24/30. In addition, the pes planovalgus deformity was identified in his feet. Brain magnetic resonance imaging (MRI) showed cerebellar atrophy without any vascular lesions. There was no abnormal finding on Tc-99m-hexamethylpropylenamineoxime (HMPAO) single photon emission computed tomography (SPECT) during the hemiplegic attack on the right side. 
 Whole exome sequencing revealed a heterozygous G947R variant in the ATP1A3 gene (c.2839G> C, read depth = 54; rs398122887), which is a known pathologic variant. The patient was treated with 5 mg of flunarizine three times per day, but this treatment was not effective and the patient discontinued because of dizziness.

Conclusion: This is an atypical AHC case with cerebellar atrophy and pes planovalgus deformity. This case demonstrates the importance of the clinical approach in diagnosing AHC and other ATP1A3-related disorders.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/atypical-alternating-hemiplegia-of-childhood-in-korea-a-case-report/