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N-methyl-D-aspartate receptors (NMDARs) mediate a slow component of excitatory synaptic transmission that plays important roles in normal brain function and development. A large number of disease-associated variants in the GRIN gene family encoding NMDAR GluN subunits have been identified in patients with various neurological and neuropsychiatric disorders. Many of these variants reduce the function of NMDARs by a range of different mechanisms, including
reduced glutamate potency, reduced glycine potency, accelerated deactivation time course, reduced current response amplitude, decreased surface expression, and/or reduced open probability. This talk will focus on three positive allosteric modulators of NMDAR receptor function (24(S)-hydroxycholesterol, pregnenolone sulfate, tobramycin) and two co-agonists (D-serine and D-cycloserine) on their ability to mitigate the diminished function of NMDARs harboring GRIN variants. We examined the effects of these modulators on NMDARs that contained 24 different loss-of-function missense variants in GRIN1, GRIN2A, or GRIN2B. The clinical phenotypes of the patients hosting these variants include epilepsy/seizures and/or developmental delay/intellectual disability. Some patients have autistic behavior or show symptoms of ADHD. For all variants, some aspect of the
reduced function was partially restored. Moreover, some variants showed enhanced sensitivity to positive allosteric modulators compared to wild type receptors. These results raise the possibility that enhancement of NMDAR function by positive allosteric modulators may be a useful therapeutic strategy.