Most higher functions of the central nervous system, including perception, cognition, and learning, rely on fast synaptic excitatory neurotransmission utilizing the neurotransmitter L-glutamate (Glu) and three structurally related classes of ionotropic Glu receptors (iGluRs) referred to as α-amino-3-hydroxy-5methyl-4-isoxazole propionic acid receptors (AMPARs), N-methyl-D-aspartic acid receptors (NMDARs), and kainate receptors (KARs). De novo and inherited missense mutations in the genes encoding iGluR receptor subunits are associated with a wide spectrum of disorders, including neurodevelopmental disorder (NDD) with epilepsy, cognitive impairment, and behavioral problems. The excitatory Glu signalling is mostly driven by AMPAR (α-amino-3-hydroxy-5methyl-4-isoxazole propionic acid) and NMDAR (N-methyl-D-aspartic acid) receptors. In contrast to NMDAR receptors, the role of AMPARs in human disorders has been less well characterized,. Functional evaluation for NMDAR has revealed that while some genetic variants cause a loss-of-function (LoF) of the receptor, other result in a gain-of-function (GoF). Knowledge about LoF versus GoF is fundamental for translational medicine and has great importance for the drugs offered to affected human subjects. The AMPARs are encoded by GRIA1-4 genes. We want to functionally characterize genetic variants in these genes found in subjects with epilepsy and NDD. This will show if the variants cause either LoF or GoF and through drug trials, we will explore whether different classes of AMPAR drugs can reverse the LoF/GoF effects of the variants to potentially provide disease-targeted treatment.
Our specific aims are:
A. Identify affected subjects with rare GRIA missense variants and collect relevant patient data to establish a database of high-quality genetic and clinical data sets.
B. Systematically evaluate the impact of GRIA variants on key parameters of AMPAR function using a combination of high-throughput biochemical and functional assays and advanced electrophysiology to pinpoint exact phenotypical mutational impact on AMPAR molecular function and classify pathogenicity of variants.
C. Analyze correlations between patient disease phenotypes and specific effects on receptor function to establish genotype-phenotype patterns and perform pilot experiments to explore options for rescue pharmacology using existing AMPAR drugs.
GRIA1/GRIA2/GRIA3/GRIA4