Key result
Two new homozygous ADARB1 variants associated with childhood seizures showed reduced (up to 60% retained) or eliminated RNA editing activity at the GRIA2 Q/R site in cell cultures.
Why the study?
Rare biallelic variants in ADARB1 cause severe infant and childhood seizures and developmental delays, prompting the identification of novel variants and characterization of their editing effects.
Novel ADARB1 variants associated with severe childhood seizures reduce RNA editing at the GRIA2 Q/R site, increasing AMPA receptor calcium permeability.
ADARB1 variants may warrant inclusion in epilepsy gene panels; leaves open whether restoring GRIA2 editing offers therapeutic benefit.
The ADARB1 gene encodes the adenosine deaminase acting on RNA 2 (ADAR2) RNA editing enzyme, which edits the GRIA2 transcript Q/R editing site with almost 100% efficiency in the nervous system. The edited GRIA2 R transcript encodes the GLUA2 R subunit isoform of tetrameric α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, which is essential to prevent seizures associated with aberrantly elevated AMPA receptor cation permeability. Rare biallelic variants in ADARB1 cause severe infant and childhood seizures and developmental delays in seven cases we previously described. Here, we report two new homozygous ADARB1 variants and study ADAR2 variant editing activities at the GRIA2 Q/R site and other editing sites in cell cultures. One new variant in the second double-stranded RNA binding domain (dsRBD II) retains up to 60% editing activity, whereas another, in the deaminase domain, eliminates RNA editing activity. Reduced GRIA2 Q/R site editing increases AMPA receptor permeability by upregulating the expression of the GLUA2 Q isoform and reducing overall GLUA2 subunit levels, resulting in AMPA receptors that lack GLUA2 and are calcium-permeable. Because failure to edit the GRIA2 Q/R site leads to failure of intron 11 splicing, we also examined the effects of ADAR2 variants on the splicing of a mouse Gria2-based reporter and concluded that ADAR2 variants affect splicing only through their effects on RNA editing activity. To expand the number of variants in ADARB1, some variants reported in ClinVar have also been analyzed by in silico methods to predict which are likely to be most deleterious and associated with seizures in patients.
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Du et al. (2025) studied Seizures, intellectual disability, and motor delay. ADARB1 variants was evaluated on RNA editing activity at the GRIA2 Q/R site. Two new homozygous ADARB1 variants associated with childhood seizures showed reduced (up to 60% retained) or eliminated RNA editing activity at the GRIA2 Q/R site in cell cultures.
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