An E280K Missense Variant in KCND3/Kv4.3-Case Report and Functional Characterization

Area of Science:

• Genetics
• Neuroscience
• Channelopathies

Background:

• Mutations in KCND3, encoding the Kv4.3 potassium channel, are linked to spinocerebellar ataxia type 19/22 (SCA19/22) and cardiac arrhythmias.
• SCA19/22 typically presents with ataxia, Parkinsonism, and peripheral neuropathy, sometimes with intellectual disability.

Observation:

• A five-year-old girl presented with headaches, clumsiness, and transient gait issues.
• Exome sequencing identified a novel KCND3 variant (c.838G>A, p.E280K) in affected family members (father and twin sisters), but not in unaffected relatives.
• Affected sisters showed mild developmental delay and impaired fluid reasoning, while unaffected family members and affected individuals lacked ataxia or Parkinsonism.

Findings:

• Electrophysiology experiments in Xenopus oocytes revealed that the Kv4.3 E280K variant alters channel activation and inactivation properties.
• The variant caused a rightward shift in voltage-activation and steady-state inactivation curves, indicating altered channel gating.
• Maximal peak current amplitudes remained similar across genotypes (WT/WT, WT/E280K, E280K/E280K).

Implications:

• The Kv4.3 E280K variant is associated with mild developmental delay and altered potassium channel function.
• Despite the known association of KCND3 mutations with severe neurological and cardiac conditions, this specific variant appears relatively benign, lacking overt ataxia or cardiac arrhythmias.
• This finding expands the phenotypic spectrum of KCND3 variants and highlights the complexity of genotype-phenotype correlations in channelopathies.