Child Neurology: PRRT2-associated movement disorders and differential diagnoses.

Paroxysmal kinesigenic dyskinesia (PKD) (MIM 128200) is a rare paroxysmal movement disorder that occurs at an estimated prevalence of 1:150,000 individuals. Onset is most commonly in childhood or adolescence, with sporadic and familial cases being reported. PKD is characterized by short and frequent episodes of dystonic or choreiform movements that are precipitated by sudden voluntary movements or startle. Classic clinical criteria for PKD therefore include an identifiable kinesigenic trigger, short duration of attacks, no loss of consciousness or pain during attacks, normal interictal neurologic examination results, the exclusion of other organic diseases, onset between 1 and 20 years of age (if no family history), and a response to treatment with anticonvulsants (sodium channel blockers). Genetically, most cases of PKD are caused by autosomal-dominant mutations in the PRRT2 (proline-rich transmembrane protein 2; DYT10) gene, making PKD part of an evolving spectrum of PRRT2-associated diseases that includes benign familial infantile seizures, infantile convulsions with choreoathetosis, episodic ataxia, hemiplegic migraine, and benign paroxysmal torticollis of infancy (table 1 and table e-1 on theNeurology® Web site at Neurology.org). We briefly review the clinical presentation and genetics of movement disorders associated with PRRT2 mutations and report an illustrative case that highlights typical and atypical features as well as important differential diagnoses in a family with PRRT2-associated PKD.