Long-term follow-up and novel genotype-phenotype analysis of monozygotic twins with ATP1A3 mutation in Alternating Hemiplegia of Childhood-2

Alternating Hemiplegia of Childhood (AHC) is a rare disorder characterized by frequent, transient attacks of hemiplegia involving either side of the body or both in association to several other disturbances including dystonic spells, abnormal ocular movements, autonomic manifestations, epileptic seizures and cognitive impairment. The clinical manifestations usually start before the age of 18 months. Two forms of the disorder known as AHC-1 (MIM#104290) and AHC-2 (MIM#614820) depends on mutations in ATP1A2 and ATP1A3 genes respectively, with over 75% of AHC caused by a mutation in the ATP1A3 gene. Herewith, we report serial clinical follow-up data of monozygotic (MZ) twin sisters, who presented in early life bath-induced dystonia, signs of acute encephalopathy at the age of 2 years, hemiplegic spells, and motor dysfunction after the age of 3 years, and in young/adult frequent episodes of headache with drastic reduction of paroxysmal motor attacks. The molecular analysis revealed a known pathogenic variant p.Asn773Ser (rs606231437) in ATP1A3 gene associated with an unusual and moderate AHC-2 phenotype, with mild cognitive impairment and lack of epilepsy. The aim of this study is to analyze the clinical phases of the MZ twins, and to investigate the novel genotype–phenotype correlation.