Paroxysmal Kinesigenic Dyskinesia and Progressive Ataxia‐Spasticity Syndrome Caused by a Biallelic Variant in KCNJ10

Biallelic KCNJ10 variants, encoding the Kir4.1 potassium channel, can cause cerebellar ataxia variably associated with intellectual disability, renal tubulopathy, sensorineural hearing loss and epilepsy (EAST or SeSAME syndrome, MIM:612780). 1,2 The predominant movement disorder, cerebellar ataxia, is typically non-progressive, though dystonic posturing occurs. 3 Genotype – phenotype correlations are poorly known. 1,3 Both monoallelic and biallelic KCNJ10 variants can cause paroxysmal kinesigenic dyskinesia (PKD), de fi ned by brief dystonic or choreic attacks triggered by sudden movements, as a predominant manifestation. 4 – 6 Notably, paroxysmal features resembling PKD were retrospectively identi fi ed in one of three previously reported siblings carrying the homozygous p.(Ile60Thr) variant. 6,7 We report a patient with biallelic KCNJ10 variant presenting with PKD and progressive ataxia-spasticity.