Proline-rich Transmembrane Protein 2 Gene Mutation in a Sporadic Paroxysmal Kinesigenic Dyskinesia.

Dear Sir,

A 12-year-old boy presented with paroxysmal events for the last 3 months. He had no adverse perinatal events and was developmentally normal. He experienced brief episodes (20–60 s) of abnormal posturing of upper and lower limbs, usually on the right side. These episodes were triggered by sudden movements like sudden rise from sitting or lying position and sometimes by startle. There was absent premonitory sensation, preserved consciousness during the events, and no “postictal” drowsiness. The frequency was variable from 3 to 5 episodes/day to once in 2–3 days. There were no other body movements, myoclonus, dance-like movements, neuroregression, and hearing or vision impairment. There was no history of headaches or seizures in infancy. The family history was unremarkable for any seizures, movement disorder, or migraine.

Examination was normal. Magnetic resonance imaging of his brain and his “interictal” electroencephalogram (EEG) were normal. He had poor response to oral valproate, started by a local practitioner. A possibility of paroxysmal kinesigenic dyskinesia (PKD) was considered in view of sudden movement/startle-induced paroxysmal dyskinesia. He had complete resolution of symptoms on oxcarbazepine. By direct sequencing of the entire coding region and exon-intron boundaries of the proline-rich transmembrane protein 2 (PRRT2) gene, the heterozygous mutation, c. 649dupC p. Arg217Profs*8 mutation, was identified in the patient. This mutation has been previously reported in patients with PKD from several parts of the world.[1]

PKD or DYT10, a rare movement disorder, may be sporadic or familial (autosomal dominant with incomplete penetrance). PRRT2 is the major gene responsible for PKD.[2] The encoded protein, PRRT2, has presynaptic localization and appears to be involved in exocytosis and neurotransmitter release.

The classical PKD phenotype is characterized by onset in childhood or adolescence; frequent brief attacks of dystonia, choreoathetosis, and/or ballismus with preserved consciousness; precipitation by sudden voluntary movements or startle; frequent aura; normal interictal neurological examination; and excellent response to anticonvulsants.[345] The most effective drugs in PKD are voltage-gated sodium channel blockers (carbamazepine, oxcarbazepine, phenytoin, lacosamide).

The common misdiagnosis is epilepsy, but preserved consciousness during the attacks, absence of postictal state, and absence of “ictal” EEG abnormalities favor PKD.

The spectrum of PRRT2-associated diseases also includes benign familial infantile seizures, infantile convulsions with choreoathetosis, episodic ataxia, hemiplegic migraine, and benign paroxysmal torticollis of infancy.[2]

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