We present a case of episodic ataxia and electrophysiologic myokymia in a young male with a KCNA1 variant found on whole exome sequencing.

The KCNA1 gene on chromosome 12p encodes a voltage gated delayed potassium channel, Kv1.1. These potassium channels are found primarily in the central nervous system, and are involved in the regulation of membrane potential and neuronal signaling. Pathogenic variations in KCNA1 have been implicated in a variety of human diseases, and have shown much heterogeneity in the phenotypic clinical spectrum. Over 20 variations in KCNA1 have been found to cause episodic ataxia type 1 (EA1), but phenotypes also include isolated myokymia and epilepsy.

A four-year-old boy presented with painful dystonic episodes involving the lower extremities, lasting hours to days. The onset of symptoms was at two years of age. The dystonic episodes were usually precipitated by illness, and were severe and progressive. Continuous myokymia was noted on electromyography (EMG). The patient has responded to treatment with carbamazepine daily and lorazepam prn.

A novel KCNA1 variant: c.941T>C (p.Ile314Thr) was revealed by whole exome sequencing.  It was inherited from his father, who reported episodic ataxia and migraine variant.

KCNA1 Variant c.41T>C (p.Ile314Thr) should be considered in patients presenting at an early age with painful dystonic episodes and electrophysiologic myokymia. Whole exome sequencing may be done to confirm the diagnosis for this potentially treatable disorder.  The regimen of scheduled carbamazepine and prn lorazepam should be considered for management.