GRIN2A-related disorders: genotype and functional consequence predict phenotype.

Area of Science:

• Neuroscience
• Genetics
• Developmental Biology

Background:

• Alterations in the N-methyl-d-aspartate receptor (NMDAR) subunit GluN2A, encoded by GRIN2A, are linked to neurodevelopmental disorders with speech and epilepsy features.
• The phenotypic spectrum of GRIN2A-related disorders is broad, ranging from mild speech delays to severe epileptic encephalopathy.

Purpose of the Study:

• To comprehensively assess phenotypes in individuals with GRIN2A-related disorders.
• To investigate the relationship between variant location, NMDAR function, and clinical presentation.
• To establish a pathomechanistic model for predicting disease severity.

Main Methods:

• Phenotypic assessment using standardized questionnaires in 92 new individuals and 156 published cases (total 248).
• Classification of GRIN2A variants (missense in transmembrane/linker domains vs. amino terminal/ligand-binding domains, and null variants).
• Electrophysiological studies in patient-derived cells and rat neurons to determine NMDAR function (gain-of-function vs. loss-of-function).

Main Results:

• Pathogenic missense variants in transmembrane and linker domains (misTMD+Linker) were associated with severe developmental phenotypes and NMDAR gain-of-function.
• Missense variants in amino terminal/ligand-binding domains (misATD+LBD) and null variants led to less severe phenotypes and NMDAR loss-of-function.
• Distinct clinical spectra and NMDAR function (gain-of-function vs. loss-of-function) were observed between variant groups, confirmed in discovery and validation cohorts.

Conclusions:

• GRIN2A variants exhibit distinct pathomechanisms (gain-of-function vs. loss-of-function) correlating with clinical severity.
• A new model links variant location to NMDAR function and phenotype, aiding in severity prediction.
• This understanding may facilitate precision medicine approaches for GRIN2A-related disorders.