Key result
KCNA2 mutation linked to episodic ataxia and diverse epilepsies, expanding the known phenotypic spectrum.
Why the study?
The genetic basis and phenotypic spectrum of KCNA2 mutations causing episodic ataxia and epilepsy were not fully characterized.
What is the genetic basis and phenotypic spectrum of episodic ataxia and pharmacoresponsive epilepsy in the studied family and probands?
Observational (n=42)
What is the genetic basis and phenotypic spectrum of episodic ataxia and pharmacoresponsive epilepsy in the studied family and probands?
A novel KCNA2 mutation causes dominantly inherited episodic ataxia and mild infantile-onset seizures, expanding the phenotypic spectrum of KCNA2-related disorders.
KCNA2 variants may underlie familial episodic ataxia with seizures; leaves open expanded testing panels pending larger validation.
OBJECTIVE: To identify the genetic basis of a family segregating episodic ataxia, infantile seizures, and heterogeneous epilepsies and to study the phenotypic spectrum of KCNA2 mutations. METHODS: A family with 7 affected individuals over 3 generations underwent detailed phenotyping. Whole genome sequencing was performed on a mildly affected grandmother and her grandson with epileptic encephalopathy (EE). Segregating variants were filtered and prioritized based on functional annotations. The effects of the mutation on channel function were analyzed in vitro by voltage clamp assay and in silico by molecular modeling. KCNA2 was sequenced in 35 probands with heterogeneous phenotypes. RESULTS: The 7 family members had episodic ataxia (5), self-limited infantile seizures (5), evolving to genetic generalized epilepsy (4), focal seizures (2), and EE (1). They had a segregating novel mutation in the shaker type voltage-gated potassium channel KCNA2 (CCDS_827.1: c.765_773del; p.255_257del). A rare missense SCN2A (rs200884216) variant was also found in 2 affected siblings and their unaffected mother. The p.255_257del mutation caused dominant negative loss of channel function. Molecular modeling predicted repositioning of critical arginine residues in the voltage-sensing domain. KCNA2 sequencing revealed 1 de novo mutation (CCDS_827.1: c.890G>A; p.Arg297Gln) in a girl with EE, ataxia, and tremor. CONCLUSIONS: A KCNA2 mutation caused dominantly inherited episodic ataxia, mild infantile-onset seizures, and later generalized and focal epilepsies in the setting of normal intellect. This observation expands the KCNA2 phenotypic spectrum from EE often associated with chronic ataxia, reflecting the marked variation in severity observed in many ion channel disorders.
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Corbett et al. (2016) conducted an observational in Episodic ataxia and epilepsy (n=42). KCNA2 mutation was evaluated on Genetic basis and phenotypic spectrum of KCNA2 mutations. A KCNA2 mutation caused dominantly inherited episodic ataxia, mild infantile-onset seizures, and later generalized and focal epilepsies, expanding the known phenotypic spectrum.
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