KCNJ4 variants disrupt inward-rectifier potassium channel function and cause refractory epilepsy.

Area of Science:

• Neurogenetics
• Molecular Biology
• Channelopathies

Background:

• Epilepsy is a common neurological disorder with a significant genetic component, often involving ion channel dysfunction.
• Inwardly rectifying potassium (Kir) channels are implicated in epileptogenesis, but KCNJ4's role in human epilepsy was previously unestablished.

Purpose of the Study:

• To identify pathogenic KCNJ4 variants in individuals with refractory epilepsy.
• To functionally characterize the identified KCNJ4 variants and their impact on Kir2.3 channel activity.

Main Methods:

• Whole exome sequencing was used to identify KCNJ4 variants in four unrelated individuals.
• Two-electrode voltage-clamp recordings in Xenopus oocytes assessed functional consequences of variants.
• Western blot analysis examined protein expression levels to rule out trafficking or expression artifacts.

Main Results:

• Four rare heterozygous KCNJ4 missense variants (Gly136Ser, Val206Met, Met293Lys, Glu384Lys) were identified.
• Two variants (Gly136Ser, Glu384Lys) showed gain-of-function, increasing potassium currents.
• Two variants (Val206Met, Met293Lys) showed loss-of-function, reducing potassium currents, independent of expression levels.

Conclusions:

• KCNJ4 is identified as a novel gene associated with epilepsy.
• Both gain- and loss-of-function mechanisms of Kir2.3 channels contribute to epileptogenesis.
• This expands the genetic understanding of epilepsy and highlights the therapeutic potential of targeting Kir channel function.