Methods: Subjects with de novo missense and nonsense GRIA1 variants were identified through international collaboration. Detailed phenotypic and genetic assessments of the subjects were carried out and the pathogenicity of the variants was evaluated using electrophysiological and biochemical analyses to characterize changes in AMPAR receptor function and expression. In addition, two Xenopus gria1 CRISPR/Cas9 F0 models were established and successfully used to characterize the in vivo consequences.
Results: Seven unrelated patients with rare GRIA1 variants were identified. One patient carried a homozygous nonsense variant (p.Arg377Ter), and six had heterozygous missense mutations (p.Arg345Gln, p.Ala636Thr, p.Ile627Thr, p.Gly745Asp) of which the p.Ala636Thr variant was recurrent in three patients. The cohort revealed subjects to have a recurrent neurodevelopmental disorder mostly affecting cognition and speech. Functional evaluation of major GluA1-containing AMPAR subtypes carrying the GRIA1 variant mutations showed that three of the four missense variants profoundly perturb receptor function. The homozygous stop-gain variant completely destroys the expression of GluA1-containing AMPARs. In addition, data from the Xenopus 1 gria1 models shows transient motor deficits, an intermittent seizure phenotype and, by using a newly described method, a significant impairment to working memory in mutants.
Conclusion: These data support the first description of a new developmental disorder caused by both heterozygous and homozygous variants in GRIA1 affecting AMPAR function.
- AMPA receptor
- glutamate receptor 1
- neurodevelopmental impairment
- Xenopus, free movement pattern Y maze