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

NMDA receptors play crucial roles in excitatory synaptic transmission. Rare variants in GRIN2A encoding the GluN2A subunit are associated with a spectrum of disorders, ranging from mild speech and language delay to intractable neurodevelopmental disorders, including but not limited to developmental and epileptic encephalopathy. A de novo missense variant, p.Ser644Gly, was identified in a child with this disorder, and Grin2a knock-in mice were generated to model and extend understanding of this intractable childhood disease. Homozygous and heterozygous mutant mice exhibited altered hippocampal morphology at 2 weeks of age, and all homozygotes exhibited lethal tonic-clonic seizures by mid-third week. Heterozygous adults displayed susceptibility to induced generalized seizures, hyperactivity, repetitive and reduced anxiety behaviours, plus several unexpected features, including significant resistance to electrically-induced limbic seizures and to pentylenetetrazole induced tonic-clonic seizures. Multielectrode recordings of neuronal networks revealed hyperexcitability and altered bursting and synchronicity. In heterologous cells, mutant receptors had enhanced NMDA receptor agonist potency and slow deactivation following rapid removal of glutamate, as occurs at synapses. NMDA receptor-mediated synaptic currents in heterozygous hippocampal slices also showed a prolonged deactivation time course. Standard anti-epileptic drug monotherapy was ineffective in the patient. Introduction of NMDA receptor antagonists was correlated with a decrease in seizure burden. Chronic treatment of homozygous mouse pups with NMDA receptor antagonists significantly delayed the onset of lethal seizures but did not prevent them. These studies illustrate the power of using multiple experimental modalities to model and test therapies for severe neurodevelopmental disorders, while revealing significant biological complexities associated with GRIN2A developmental and epileptic encephalopathy.

Background:Prior studies have shown an association between high blood urea nitrogen (BUN) and an elevated risk of mortality in heart failure patients, but data on the prognostic significance of BUN and other markers of kidney function in acute ischemic stroke (AIS) patients are sparse. Methods and Results:A total of 3,355 AIS patients were enrolled from December 2013 to May 2014, across 22 hospitals. Admission BUN was divided into quartiles (Q1, <4.39 mmol/L; Q2, ≥4.39 and <5.40 mmol/L; Q3, ≥5.40 and <6.70 mmol/L and Q4, ≥6.70 mmol/L) and estimated glomerular filtration rate (eGFR), creatinine (Cr) and BUN/Cr were also categorized. Cox proportional hazard and logistic regression models were used to estimate the effect of BUN, eGFR, Cr and BUN/Cr on all-cause in-hospital mortality and poor outcome on discharge (modified Rankin Scale score ≥3) in AIS patients. During hospitalization, 120 patients (3.6%) died from all causes and 1,287 (38.4%) had poor outcome at discharge. BUN was independently associated with all-cause in-hospital mortality (adjusted HR for Q4 vs. Q1, 3.75; 95% CI: 1.53-9.21; P-trend=0.003) but not poor outcome at discharge (P-trend=0.229). No significant association was found, however, between reduced eGFR, increased Cr and BUN/Cr and all-cause in-hospital mortality and poor outcome at discharge (all P-trend ≥0.169). Conclusions:Increased BUN at admission is a significant prognostic factor associated with in-hospital mortality in AIS patients, but not with poor discharge outcome.