De novo GRIN variants in M3 helix associated with neurological disorders control channel gating of NMDA receptor.

N-methyl-D-aspartate receptors (NMDARs) are members of the glutamate receptor family and participate in excitatory postsynaptic transmission throughout the central nervous system. Genetic variants in GRIN genes encoding NMDAR subunits are associated with a spectrum of neurological disorders. The M3 transmembrane helices of the NMDAR couple directly to the agonist-binding domains and form a helical bundle crossing in the closed receptors that occludes the pore. The M3 functions as a transduction element whose conformational change couples ligand binding to opening of an ion conducting pore. In this study, we report the functional consequences of 48 de novo missense variants in GRIN1, GRIN2A, and GRIN2B that alter residues in the M3 transmembrane helix. These de novo variants were identified in children with neurological and neuropsychiatric disorders including epilepsy, developmental delay, intellectual disability, hypotonia and attention deficit hyperactivity disorder. All 48 variants in M3 for which comprehensive testing was completed produce a gain-of-function (28/48) compared to loss-of-function (9/48); 11 variants had an indeterminant phenotype. This supports the idea that a key structural feature of the M3 gate exists to stabilize the closed state so that agonist binding can drive channel opening. Given that most M3 variants enhance channel gating, we assessed the potency of FDA-approved NMDAR channel blockers on these variant receptors. These data provide new insight into the structure-function relationship of the NMDAR gate, and suggest that variants within the M3 transmembrane helix produce a gain-of-function.

Usefulness of transpedal intervention for inferior epigastric artery bleeding following catheter ablation: a case report.

Background: Cardiovascular interventions may result in access-site complication, including inferior epigastric artery (IEA) bleeding. The IEA injury is generally treated through surgery and transcatheter embolization; however, additional complications should be avoided in the bailout procedure. Here, we present a case of catheter ablation complicated by IEA haemorrhage that we managed by transcatheter embolization using a transpedal intervention (TPI). Case summary: A 58-year-old man underwent catheter ablation for symptomatic paroxysmal atrial fibrillation. Pulmonary vein isolation was performed uneventfully via catheterization of the right femoral artery and vein access. After the procedure, he complained of persistent abdominal pain and had a palpable mass in the lower right abdomen. Computed tomography angiography (CTA) revealed a haematoma in the right rectus abdominis with signs of active bleeding from a branch of the right IEA. We performed transcatheter arterial embolization through a TPI to stop bleeding and avoid further complication. No leakage of contrast media was detected after embolization using a microcoil and the abdominal pain improved. We did not observe any serious intraprocedural complications. Discussion: Catheter ablation procedures may be complicated by access-site complications such as active bleeding. Arterial embolization is a feasible treatment approach to control the resulting haemorrhage. Embolization through the transpedal route (TPI) could be an effective bailout technique in the setting of emergent transcatheter arterial embolization to achieve haemostasis and avoid further complication.

Trans-coronary pacing via Rota wire prevents bradycardia during rotational atherectomy: a case report.

Back ground: Rotational atherectomy (RA) is used for plaque modification in patients with heavily calcified coronary lesions. Rotational atherectomy can induce significant bradycardia or atrioventricular block requiring for temporary pacemaker insertion. In this report, we present a case of trans-coronary pacing via a Rota wire to prevent bradycardia during RA in the proximal right coronary artery (RCA). Case summary: A 72-year-old woman with a 1 month history of worsening effort angina was admitted to our hospital. Computed tomography coronary angiography disclosed significant coronary stenosis with severe calcification in proximal RCA. Coronary angiography revealed significant coronary stenosis with severe calcification in the proximal RCA. Subsequently, percutaneous coronary artery intervention was performed under the guidance of intravascular ultrasound (IVUS). The pull-back IVUS showed a circumferential calcified lesion in the proximal RCA that was treated using RA, which induced significant bradycardia requiring temporary pacemaker insertion. Immediately, trans-coronary pacing was provided via a Rota wire placed in the far distal RCA; this was used for back-up pacing during RA. Rotational atherectomy was completed by safely modifying the calcified lesion. After successful debulking of the calcified lesion, we dilated with a balloon, and a drug-eluting stent was implanted at the proximal RCA. Final IVUS and angiography showed good stent apposition and expansion. We did not observe any serious intraprocedural complications. Discussion: Rotational atherectomy is used for plaque modification in patients with heavily calcified coronary lesions. Rotational atherectomy can induce significant bradycardia or atrioventricular block requiring for temporary pacemaker insertion via the transvenous route. This method could be an effective method to prevent bradycardia during RA.

A novel treatment using a guide extension catheter and distal protection device for refractory coronary embolism: case report.

BACKGROUND: A large thrombus burden in patients with acute myocardial infarction is associated with worse outcomes. Although various methods of thrombus aspiration have been described, there is a potential limitation in the mechanism of eliminating a thrombus with only the use of an aspiration device. In this report, we present a novel method of retrieving massive thrombus using a guide extension catheter and a filter device. CASE SUMMARY: An 80-year-old man was diagnosed with anterior ST-elevation myocardial infarction (STEMI). Emergency coronary angiography revealed that the left anterior descending artery (LAD) showed an acute thrombotic occlusion in the mid-section. The percutaneous coronary intervention was performed to recanalize an occluded LAD. Although thrombectomy using an aspiration catheter and a guide catheter extension system was performed repeatedly, only a small amount of the thrombus was retrieved, and the LAD was still occluded. Therefore, we planned to remove the large thrombus burden by capturing the entire thrombus between the tip of the guide extension catheter and distal protection device, followed by pulling them out of the guide catheter together. A large amount of red thrombus, which adhered to the axis of the filter device, was successfully retrieved. The occluded LAD was successfully recanalized without balloon dilatation or stent implantation. DISCUSSION: Although a variety of aspiration devices are available, removal of large coronary artery thrombi with the use of an aspiration catheter alone can at times prove difficult. To solve this problem, we developed a novel technique for retrieving large thrombi. This method is effective in removing refractory thrombi for the treatment of STEMI patients.

Late peri-stent contrast staining appearance due to rupture of atherogenic neointima following drug-eluting stent.

The development of peri-stent contrast staining (PSS) after coronary intervention with implantation of a stent is observed in approximately 1-3% of patients treated with drug-eluting stent. Although the cumulative incidences of late in-stent restenosis and stent thrombosis are significantly higher in lesions with PSS than in those without the finding, the mechanisms for the development of PSS have not yet been fully elucidated. In this report, we describe a case of rapid development of PSS with ulcer formation caused by rupture of atherogenic neointima, which was observed by serial optical coherence tomography examinations over 6 months. Protrusion of the stent-jailed underlying necrotic core toward the lumen by the contracting force might have resulted in formation of atherogenic neointima within the stent. Subsequently, rupture of this necrotic core induced by iatrogenic neointimal injury due to balloon dilation and dissolution of the accumulated necrotic core may have resulted in PSS formation 6 months after the procedure. These findings may be helpful for consideration of etiology and therapeutic strategy for lesions with PSS. .

Acute myocardial infarction in a patient with uncorrected tetralogy of Fallot accompanied by coronary artery ectasia: A case report.

A 63-year-old male with a medical history of uncorrected tetralogy of Fallot (TOF) presented to our hospital due to acute myocardial infarction (AMI). Emergency coronary angiography (CAG) was performed and it showed a severe thrombotic stenosis in the middle right coronary artery (RCA) and total thrombotic occlusion of the posterior descending branch of the RCA. Subsequently, percutaneous coronary artery intervention (PCI) under the guidance of intravascular ultrasound (IVUS) was performed. He was discharged on the 14th day in stable condition. Nine months after the PCI procedure, coronary computed tomography angiography was performed for follow-up, which revealed tetralogy of Fallot and complete resolution of the thrombus and ectasic coronary artery without stenosis. When he was 70 years old, he was transferred to our hospital because of recurrent AMI. As emergency CAG showed total thrombotic occlusion of the middle RCA, IVUS-guided PCI was performed. We experienced a very rare case of AMI in an adult patient with uncorrected TOF accompanied by coronary artery ectasia (CAE). To the best of our knowledge, this is the first case of AMI in an adult patient with uncorrected TOF accompanied by CAE. .

Short term outcomes of an enhanced recovery after surgery (ERAS) pathway versus a traditional discharge pathway after posterior spinal fusion for adolescent idiopathic scoliosis.

PURPOSE: Enhanced Recovery after Surgery (ERAS) pathways have been shown to decrease length of stay (LOS) after posterior spinal fusion (PSF) for adolescent idiopathic scoliosis (AIS). The aim of this study was to compare immediate post-operative outcomes following an ERAS pathway with a traditional pathway for AIS. METHODS: A prospective dual-center study of patients treated using an ERAS pathway (203 patients) or a traditional discharge (TD) pathway (73 patients) was performed with focus on pain at discharge, quality of life at one month, and return to school/work. RESULTS: LOS was 55% less in the ERAS group (4.8 days TD vs. 2.2 days ERAS, p < 0.001). Length of surgery (4.8 h TD vs. 2.8 h, p < 0.001) and EBL (500 cc vs. 240 cc, p < 0.001) were greater in the TD group, likely related to larger curve magnitudes ((62.0° TD vs. 54.0° ERAS, p < 0.001), a higher percentage of patients undergoing osteotomies (94% vs. 46%, p < 0.001) and more levels fused (11.4 ± 1.6 vs. 10.1 ± 2.6, p < 0.001) in the TD group. Regression analysis showed no difference in Visual Analog Score (VAS) score at discharge or quality of recovery using the QOR9 instrument between groups at follow up. There was no difference in return to school (p = 0.43) and parents' return to work (p = 0.61) between the groups. CONCLUSION: Patients managed with an ERAS pathway had similar pain scores at discharge than those managed with a TD pathway. Both groups showed evidence of rapid return to normalcy by the first follow up visit.

Factors Contributing to Diurnal Variation in Athletic Performance and Methods to Reduce Within-Day Performance Variation: A Systematic Review.

ABSTRACT: Kusumoto, H, Ta, C, Brown, SM, and Mulcahey, MK. Factors contributing to diurnal variation in athletic performance and methods to reduce within-day performance variation: A systematic review. J Strength Cond Res 35(12S): S119-S135, 2021-For many individuals, athletic performance (e.g., cycle ergometer output) differs based on the time of day (TOD). This study identified factors contributing to diurnal variation in athletic performance and methods to reduce TOD performance variation. Comprehensive searches of PubMed, Ovid, EMBASE, Web of Science, and Cochrane Libraries were conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Peer-reviewed publications reporting quantitative, significant diurnal variation (p ≤ 0.05) of athletic performance with explanations for the differences were included. Studies providing effective methods to reduce diurnal variation were also included. Literature reviews, studies involving nonhuman or nonadult subjects, studies that intentionally manipulated sleep duration or quality, and studies deemed to be of poor methodological quality using NIH Quality Assessment Tools were excluded. Forty-nine studies met the inclusion criteria. Body temperature differences (n = 13), electromyographic parameters (n = 10), serum biomarker fluctuations (n = 5), athlete chronotypes (n = 4), and differential oxygen kinetics (n = 3) were investigated as significant determinants of diurnal variation in sports performance. Successful techniques for reducing diurnal athletic performance variability included active or passive warm-up (n = 9), caffeine ingestion (n = 2), and training-testing TOD synchrony (n = 3). Body temperature was the most important contributor to diurnal variation in athletic performance. In addition, extended morning warm-up was the most effective way to reduce performance variation. Recognizing contributors to diurnal variation in athletic performance may facilitate the development of more effective training regimens that allow athletes to achieve consistent performances regardless of TOD.

Successful percutaneous removal of dislodged ring-marker of optical coherence tomography catheter using the twisted wire technique with a guide-extension catheter: A case report.

An 81-year-old male with diabetes and hypertension was admitted to our hospital due to chest pain on exertion. Coronary angiography revealed a severe stenosis at the middle of right coronary artery (RCA). We performed percutaneous coronary intervention under the guidance of optical coherence tomography (OCT) to the lesion in the middle RCA. After balloon dilations, a drug-eluting stent was deployed to the lesion. Then, OCT examination was performed. At that time, fluoroscopy revealed a foreign body over the 0.014-inch guidewire in the distal RCA, which was the ring-marker of OCT catheter. As RCA blood flow was well preserved, percutaneous removal of the dislodged ring-marker was immediately attempted. At first, we tried to remove the dislodged ring-marker with the guide-extension catheter trapping technique. However, it failed and advanced balloon catheter made the dislodged ring-marker migrate more distally. Therefore, we tried the twisted wire technique with the guide-extension catheter and finally the dislodged ring-marker was removed with it. To the best of our knowledge, this is the first case report of a successful percutaneous removal of a dislodged ring-marker of OCT catheter using the twisted wire technique with a guide-extension catheter. .

Management of Orthopaedic Emergencies During a Pandemic: Compartment Syndrome of the Hand in a Patient with COVID-19: A Case Report.

CASE: A 58-year-old man presented with acute respiratory distress syndrome and coagulopathy secondary to COVID-19. He developed acute compartment syndrome (ACS) of the left hand. He underwent a bedside 10-compartment decompression of the hand with volar forearm and carpal tunnel release while in the ICU. This report adds to the scarce body of literature regarding orthopaedic complications related to COVID-19. CONCLUSION: Coagulopathy secondary to COVID-19 can be a risk factor for the development of ACS. Frequent examinations of lines, restraints, and extremities are recommended. The COVID-19 pandemic presents unique challenges, necessitating clinical adjustments to best care for patients.

Effect of neointimal tissue morphology on vascular response to balloon angioplasty in lesions with in-stent restenosis after drug-eluting stent deployment: an optical coherence tomography analysis.

This study aimed to evaluate the vascular response to balloon angioplasty for drug-eluting stent (DES) in-stent restenosis (ISR) lesions based on our novel optical coherence tomography (OCT) classification to establish the optimal treatment strategy for ISR lesions after DES implantation. A total of 104 ISR lesions after DES implantation were imaged by OCT and categorized into the following six patterns: type I-homogeneous high-intensity tissue, type II-heterogeneous tissue with signal attenuation, type III-speckled heterogeneous tissue, type IV-mixed tissue containing poorly delineated region with invisible strut, type V-mixed tissue containing sharply delineated low-intensity region, and type VI-bright protruding tissue with an irregular surface. Serial volumetric OCT analysis was performed before and after balloon dilation to evaluate the vascular response to balloon angioplasty. After balloon dilation, the minimal decrease in neointimal volume was noted in type I lesions and maximal in type III lesions. In contrast, the increase in stent volume was significantly more in type I lesions than others. Neointimal tissue characterization by OCT allows us to provide useful information about the vascular response to balloon dilation, which can influence the therapeutic strategy for DES ISR lesions.

Optical coherence tomography characteristics of in-stent restenosis after drug-eluting stent implantation: a novel classification and its clinical significance.

This study aimed to establish a novel classification of in-stent restenosis (ISR) morphological characteristics after drug-eluting stent (DES) implantation as visualized by optical coherence tomography (OCT) and determine its clinical significance. A total of 133 lesions with intrastent restenosis after DES implantation were imaged by OCT. Neointimal tissue characteristics were categorized according to the classical classification as either homogeneous, heterogeneous, or layered. Then all tissues were also classified into six types as follows: homogeneous high-intensity tissue (type I), heterogeneous tissue with signal attenuation (type II), speckled heterogeneous tissue (type III), heterogeneous tissue containing poorly delineated region with invisible strut (type IV), heterogeneous tissue containing sharply delineated low-intensity region (type V), or bright protruding tissue with an irregular surface (type VI). The kappa value for interobserver agreement between the two observers was higher in the modified classification than in the classical classification (0.97 and 0.72, respectively). Most lesions classified as type V and VI were likely to be identified in patients on hemodialysis and located at the ostial right coronary artery. The duration from stent implantation to ISR was significantly longer in types IV and VI than in others. The incidence of stent fracture was significantly higher in types I and IV. This new modified classification enabled us to classify most ISR lesions easily with higher reproducibility. The clinical significance of neointimal restenotic tissue classification by OCT became clear while using the modified classification.

Heterogeneous clinical and functional features of GRIN2D-related developmental and epileptic encephalopathy.

N-methyl d-aspartate receptors are ligand-gated ionotropic receptors mediating a slow, calcium-permeable component of excitatory synaptic transmission in the CNS. Variants in genes encoding NMDAR subunits have been associated with a spectrum of neurodevelopmental disorders. Here we report six novel GRIN2D variants and one previously-described disease-associated GRIN2D variant in two patients with developmental and epileptic encephalopathy. GRIN2D encodes for the GluN2D subunit protein; the GluN2D amino acids affected by the variants in this report are located in the pre-M1 helix, transmembrane domain M3, and the intracellular carboxyl terminal domain. Functional analysis in vitro reveals that all six variants decreased receptor surface expression, which may underline some shared clinical symptoms. In addition the GluN2D(Leu670Phe), (Ala675Thr) and (Ala678Asp) substitutions confer significantly enhanced agonist potency, and/or increased channel open probability, while the GluN2D(Ser573Phe), (Ser1271Phe) and (Arg1313Trp) substitutions result in a mild increase of agonist potency, reduced sensitivity to endogenous protons, and decreased channel open probability. The GluN2D(Ser573Phe), (Ala675Thr), and (Ala678Asp) substitutions significantly decrease current amplitude, consistent with reduced surface expression. The GluN2D(Leu670Phe) variant slows current response deactivation time course and increased charge transfer. GluN2D(Ala678Asp) transfection significantly decreased cell viability of rat cultured cortical neurons. In addition, we evaluated a set of FDA-approved NMDAR channel blockers to rescue functional changes of mutant receptors. This work suggests the complexity of the pathological mechanisms of GRIN2D-mediated developmental and epileptic encephalopathy, as well as the potential benefit of precision medicine.

Utility and Validity of Intracoronary Administration of Nicorandil Alone for the Measurement of Fractional Flow Reserve in Patients With Intermediate Coronary Stenosis.

BACKGROUND: Intracoronary (IC) administration of nicorandil has been proposed as an alternative choice of hyperemic agent for fractional flow reserve (FFR) measurements. This study evaluated the utility and validity of IC nicorandil administration alone to induce maximal hyperemia.Methods and Results:Two-hundred-seven patients with coronary artery disease listed for coronary angiography with FFR were prospectively enrolled. FFR was measured after (1) IC administration of nicorandil 2 mg (ICNIC2 mg); (2) continuous intravenous (IV) adenosine triphosphatase (ATP) infusion at 150 µg/kg/min (IVATP150); (3) IV ATP infusion at 210 µg/kg/min (IVATP210); (4) IC administration of 0.5 mg nicorandil during IVATP150 (ICNIC0.5 mg+IVATP150); (5) IC administration of 1 mg nicorandil during IVATP150 (ICNIC1 mg+IVATP150); and (6) IC administration of 2 mg nicorandil during IVATP150 (ICNIC2 mg+IVATP150). The average FFR values and the rate of achieving maximum hyperemia after ICNIC2 mg, IVATP150, IVATP210, ICNIC0.5 mg+IVATP150, ICNIC1 mg+IVATP150, and ICNIC2 mg+IVATP150 were 0.85±0.08, 0.89±0.08, 0.85±0.09, 0.84±0.08, 0.83±0.08, 0.83±0.08 (P<0.01), and 92%, 54%, 91%, 96%, 99%, 99% (P<0.01), respectively. The incidence of systolic aortic pressure drop, chest discomfort, and transient atrioventricular block increased in a dose-dependent manner after IV ATP infusion, but almost no adverse effects were observed after ICNIC2 mg. CONCLUSIONS: ICNIC2 mg produced a more pronounced hyperemia than continuous IV ATP, and might be the preferred method for assessment of FFR.

De novo GRIN variants in NMDA receptor M2 channel pore-forming loop are associated with neurological diseases.

N-methyl-D-aspartate receptors (NMDARs) mediate slow excitatory postsynaptic transmission in the central nervous system, thereby exerting a critical role in neuronal development and brain function. Rare genetic variants in the GRIN genes encoding NMDAR subunits segregated with neurological disorders. Here, we summarize the clinical presentations for 18 patients harboring 12 de novo missense variants in GRIN1, GRIN2A, and GRIN2B that alter residues in the M2 re-entrant loop, a region that lines the pore and is intolerant to missense variation. These de novo variants were identified in children with a set of neurological and neuropsychiatric conditions. Evaluation of the receptor cell surface expression, pharmacological properties, and biophysical characteristics show that these variants can have modest changes in agonist potency, proton inhibition, and surface expression. However, voltage-dependent magnesium inhibition is significantly reduced in all variants. The NMDARs hosting a single copy of a mutant subunit showed a dominant reduction in magnesium inhibition for some variants. These variant NMDARs also show reduced calcium permeability and single-channel conductance, as well as altered open probability. The data suggest that M2 missense variants increase NMDAR charge transfer in addition to varied and complex influences on NMDAR functional properties, which may underlie the patients' phenotypes.

The GluN2B-Glu413Gly NMDA receptor variant arising from a de novo GRIN2B mutation promotes ligand-unbinding and domain opening.

N-methyl-D-aspartate (NMDA) receptors are transmembrane glutamate-binding ion channels that mediate neurotransmission in mammals. NMDA receptor subunits are tetrameric complexes of GluN1 and GluN2A-D subunits, encoded by the GRIN gene family. Of these subunits, GluN2B is suggested to be required for normal development of the central nervous system. A mutation identified in a patient with developmental delay, E413G, resides in the GluN2B ligand-binding domain and substantially reduces glutamate potency by an unknown mechanism. GluN2B Gly413, though near the agonist, is not in van der Waals contact with glutamate. Visual analysis of the GluN2B structure with the E413G mutation modeled suggests that replacement of Glu with Gly at this position increases solvent access to the ligand-binding domain. This was confirmed by molecular modeling, which showed that the ligand is more mobile in GluN2B-E413G than WT GluN2B. Evaluation of agonist occupancy using random accelerated molecular dynamics (RAMD) simulations predicts that the glutamate exits the binding-site more rapidly for GluN2B-E413G than WT receptors. This analysis was extended to other binding-site mutations, which produced qualitative agreement between experimentally determined EC50 values, deactivation time constants, and ligand motion within the binding-site. Furthermore, long sub-microsecond molecular dynamics simulations of the bi-lobed ligand-binding domain revealed that it adopted a cleft-open ligand-free state more often for GluN2B-E413G than wild-type GluN2B. This is consistent with the idea that L-glutamate binding is altered such that the ligand-binding domain occupies the open-cleft conformation associated with the closed channel.

An NMDAR positive and negative allosteric modulator series share a binding site and are interconverted by methyl groups.

N-methyl-d-aspartate receptors (NMDARs) are an important receptor in the brain and have been implicated in multiple neurological disorders. Many non-selective NMDAR-targeting drugs are poorly tolerated, leading to efforts to target NMDAR subtypes to improve the therapeutic index. We describe here a series of negative allosteric NMDAR modulators with submaximal inhibition at saturating concentrations. Modest changes to the chemical structure interconvert negative and positive modulation. All modulators share the ability to enhance agonist potency and are use-dependent, requiring the binding of both agonists before modulators act with high potency. Data suggest that these modulators, including both enantiomers, bind to the same site on the receptor and share structural determinants of action. Due to the modulator properties, submaximal negative modulators in this series may spare NMDAR at the synapse, while augmenting the response of NMDAR in extrasynaptic spaces. These modulators could serve as useful tools to probe the role of extrasynaptic NMDARs.

A novel missense mutation in GRIN2A causes a nonepileptic neurodevelopmental disorder.

BACKGROUND: Mutations in the GRIN2A gene, which encodes the GluN2A (glutamate [NMDA] receptor subunit epsilon-1) subunit of the N-methyl-d-aspartate receptor, have been identified in patients with epilepsy-aphasia spectrum disorders, idiopathic focal epilepsies with centrotemporal spikes, and epileptic encephalopathies with severe developmental delay. However, thus far, mutations in this gene have not been associated with a nonepileptic neurodevelopmental disorder with dystonia. OBJECTIVES: The objective of this study was to identify the disease-causing gene in 2 siblings with neurodevelopmental and movement disorders with no epileptiform abnormalities. METHODS: The study method was targeted next-generation sequencing panel for neuropediatric disorders and subsequent electrophysiological studies. RESULTS: The 2 siblings carry a novel missense mutation in the GRIN2A gene (p.Ala643Asp) that was not detected in genomic DNA isolated from blood cells of their parents, suggesting that the mutation is the consequence of germinal mosaicism in 1 progenitor. In functional studies, the GluN2A-A643D mutation increased the potency of the agonists L-glutamate and glycine and decreased the potency of endogenous negative modulators, including protons, magnesium and zinc but reduced agonist-evoked peak current response in mammalian cells, suggesting that this mutation has a mixed effect on N-methyl-d-aspartate receptor function. CONCLUSION: De novo GRIN2A mutations can give rise to a neurodevelopmental and movement disorder without epilepsy. © 2018 International Parkinson and Movement Disorder Society.

De novo mutations in GRIN1 cause extensive bilateral polymicrogyria.

Polymicrogyria is a malformation of cortical development. The aetiology of polymicrogyria remains poorly understood. Using whole-exome sequencing we found de novo heterozygous missense GRIN1 mutations in 2 of 57 parent-offspring trios with polymicrogyria. We found nine further de novo missense GRIN1 mutations in additional cortical malformation patients. Shared features in the patients were extensive bilateral polymicrogyria associated with severe developmental delay, postnatal microcephaly, cortical visual impairment and intractable epilepsy. GRIN1 encodes GluN1, the essential subunit of the N-methyl-d-aspartate receptor. The polymicrogyria-associated GRIN1 mutations tended to cluster in the S2 region (part of the ligand-binding domain of GluN1) or the adjacent M3 helix. These regions are rarely mutated in the normal population or in GRIN1 patients without polymicrogyria. Using two-electrode and whole-cell voltage-clamp analysis, we showed that the polymicrogyria-associated GRIN1 mutations significantly alter the in vitro activity of the receptor. Three of the mutations increased agonist potency while one reduced proton inhibition of the receptor. These results are striking because previous GRIN1 mutations have generally caused loss of function, and because N-methyl-d-aspartate receptor agonists have been used for many years to generate animal models of polymicrogyria. Overall, our results expand the phenotypic spectrum associated with GRIN1 mutations and highlight the important role of N-methyl-d-aspartate receptor signalling in the pathogenesis of polymicrogyria.

The Bioactive Protein-Ligand Conformation of GluN2C-Selective Positive Allosteric Modulators Bound to the NMDA Receptor.

N-methyl-d-aspartate (NMDA) receptors are ligand-gated, cation-selective channels that mediate a slow component of excitatory synaptic transmission. Subunit-selective positive allosteric modulators of NMDA receptor function have therapeutically relevant effects on multiple processes in the brain. A series of pyrrolidinones, such as PYD-106, that selectively potentiate NMDA receptors that contain the GluN2C subunit have structural determinants of activity that reside between the GluN2C amino terminal domain and the GluN2C agonist binding domain, suggesting a unique site of action. Here we use molecular biology and homology modeling to identify residues that line a candidate binding pocket for GluN2C-selective pyrrolidinones. We also show that occupancy of only one site in diheteromeric receptors is required for potentiation. Both GluN2A and GluN2B can dominate the sensitivity of triheteromeric receptors to eliminate the actions of pyrrolidinones, thus rendering this series uniquely sensitive to subunit stoichiometry. We experimentally identified NMR-derived conformers in solution, which combined with molecular modeling allows the prediction of the bioactive binding pose for this series of GluN2C-selective positive allosteric modulators of NMDA receptors. These data advance our understanding of the site and nature of the ligand-protein interaction for GluN2C-selective positive allosteric modulators for NMDA receptors.