Two de novo GluN2B mutations affect multiple NMDAR-functions and instigate severe pediatric encephalopathy
- Technion- Israel Institute of Technology, Israel
- Clalit health services, Israel
- Rambam medical center, Israel
- Tel Aviv University, Israel
- University of Southern Denmark, Denmark
Abstract
The N-methyl-D-aspartate receptors (NMDARs; GluNRS) are glutamate receptors, commonly located at excitatory synapses. Mutations affecting receptor function often lead to devastating neurodevelopmental disorders. We have identified two toddlers with different heterozygous missense mutations of the same, and highly conserved, glycine residue located in the ligand-binding-domain of GRIN2B: G689C and G689S. Structure simulations suggest severely impaired glutamate binding which we confirm by functional analysis. Both variants show three-orders of magnitude reductions in glutamate EC50, with G689S exhibiting the largest reductions observed in GRIN2B (~2000-fold). Moreover, variants multimerize with, and upregulate, GluN2Bwt-subunits, thus engendering a strong dominant-negative effect on mixed channels. In neurons, overexpression of the variants instigates suppression of synaptic GluNRs. Lastly, while exploring spermine potentiation as a potential treatment, we discovered that the variants fail to respond due to G689's novel role in proton-sensing. Together, we describe two unique variants with extreme effects on channel function. We employ protein-stability measures to explain why current (and future) LBD mutations in GluN2B primarily instigate Loss-of-Function.
Data availability
All data generated or analysed during this study are included in the manuscript and supporting files. Raw data is deposited at Dryad (doi:10.5061/dryad.1jwstqjv3)
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Two de novo GluN2B mutations affect multiple NMDAR-functions and instigate severe pediatric encephalopathyDryad Digital Repository, doi:10.5061/dryad.1jwstqjv3.
Article and author information
Author details
Funding
Israel Science Foundation (1096/17)
- Shai Berlin
Teva Pharmaceutical Industries (PR783187)
- Shai Kellner
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Animal experimentation: All Experiments were approved by the Technion Institutional Animal Care and Use Committee (permit SB, no. IL-129-09-17).
Copyright
© 2021, Kellner et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Two de novo GluN2B mutations affect multiple NMDAR-functions and instigate severe pediatric encephalopathy
eLife 10:e67555.
https://doi.org/10.7554/eLife.67555
Further reading
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Background:
Individuals with Down syndrome (DS), the genetic condition caused by trisomy 21 (T21), display clear signs of immune dysregulation, including high rates of autoimmunity and severe complications from infections. Although it is well established that T21 causes increased interferon responses and JAK/STAT signaling, elevated autoantibodies, global immune remodeling, and hypercytokinemia, the interplay between these processes, the clinical manifestations of DS, and potential therapeutic interventions remain ill defined.
Methods:
We report a comprehensive analysis of immune dysregulation at the clinical, cellular, and molecular level in hundreds of individuals with DS, including autoantibody profiling, cytokine analysis, and deep immune mapping. We also report the interim analysis of a Phase II clinical trial investigating the safety and efficacy of the JAK inhibitor tofacitinib through multiple clinical and molecular endpoints.
Results:
We demonstrate multi-organ autoimmunity of pediatric onset concurrent with unexpected autoantibody-phenotype associations in DS. Importantly, constitutive immune remodeling and hypercytokinemia occur from an early age prior to autoimmune diagnoses or autoantibody production. Analysis of the first 10 participants to complete 16 weeks of tofacitinib treatment shows a good safety profile and no serious adverse events. Treatment reduced skin pathology in alopecia areata, psoriasis, and atopic dermatitis, while decreasing interferon scores, cytokine scores, and levels of pathogenic autoantibodies without overt immune suppression.
Conclusions:
JAK inhibition is a valid strategy to treat autoimmune conditions in DS. Additional research is needed to define the effects of JAK inhibition on the broader developmental and clinical hallmarks of DS.
Funding:
NIAMS, Global Down Syndrome Foundation.
Clinical trial number:
