GRIN2D Recurrent De Novo Dominant Mutation Causes a Severe Epileptic Encephalopathy Treatable with NMDA Receptor Channel Blockers.

N-methyl-D-aspartate receptors (NMDARs) are ligand-gated cation channels that mediate excitatory synaptic transmission. Genetic mutations in multiple NMDAR subunits cause various childhood epilepsy syndromes. Here, we report a de novo recurrent heterozygous missense mutation-c.1999G>A (p.Val667Ile)-in a NMDAR gene previously unrecognized to harbor disease-causing mutations, GRIN2D, identified by exome and candidate panel sequencing in two unrelated children with epileptic encephalopathy. The resulting GluN2D p.Val667Ile exchange occurs in the M3 transmembrane domain involved in channel gating. This gain-of-function mutation increases glutamate and glycine potency by 2-fold, increases channel open probability by 6-fold, and reduces receptor sensitivity to endogenous negative modulators such as extracellular protons. Moreover, this mutation prolongs the deactivation time course after glutamate removal, which controls the synaptic time course. Transfection of cultured neurons with human GRIN2D cDNA harboring c.1999G>A leads to dendritic swelling and neuronal cell death, suggestive of excitotoxicity mediated by NMDAR over-activation. Because both individuals' seizures had proven refractory to conventional antiepileptic medications, the sensitivity of mutant NMDARs to FDA-approved NMDAR antagonists was evaluated. Based on these results, oral memantine was administered to both children, with resulting mild to moderate improvement in seizure burden and development. The older proband subsequently developed refractory status epilepticus, with dramatic electroclinical improvement upon treatment with ketamine and magnesium. Overall, these results suggest that NMDAR antagonists can be useful as adjuvant epilepsy therapy in individuals with GRIN2D gain-of-function mutations. This work further demonstrates the value of functionally evaluating a mutation, enabling mechanistic understanding and therapeutic modeling to realize precision medicine for epilepsy.

Unresponsive Wakefulness Syndrome in Children after Near-Drowning: Long-Term Outcome and Impact on the Families.

Among 131 children admitted to our institution for early phase rehabilitation after freshwater near-drowning (ND) between the year 1986 and 2000, 87 were in unresponsive wakefulness syndrome (UWS) for at least 4 weeks after the accidents. An anonymous questionnaire was sent to the families after 0.5 to 15.0 years (median: 4.6) and 48 mothers and 51 fathers of 55 of these 87 children were interviewed after 6.6 to 23.8 years (median: 13.8) of ND. At the time of the interviews, 8/55 children were able to perform daily living activities independently, 36/55 children were not able to do so (many of them suffered from chronic medical conditions like spasticity or disorders of swallowing), and 11/55 children had died. Health-related quality of life (HRQoL) was, however, similar to the normal population for mothers, and even higher for fathers. Furthermore, the ND accident had apparently not lead to a higher rate of separations of parents but had increased their likelihood to have further children. Feelings of guilt were highly prevalent (23/47 mothers, 20/47 fathers), and correlated with lower HRQoL of the respective parent. We found correlations between duty of supervision and feelings of guilt and between outcome and HRQoL for only the fathers. In conclusion, we found that after 4 weeks in UWS, the long-term neurological outcome of pediatric ND victims is often but not always poor. Despite often severe disabilities or death of the child during long-term care, parents surprisingly report little impact on their HRQoL, on the stability of their partnership or on their wish to have further children. Our findings may help parents and physicians to choose the best treatment for a child in UWS due to different etiologies striking the balance between rehabilitation and palliative care.

Mesial Temporal Sclerosis in SCN1A-Related Epilepsy: Two Long-Term EEG Case Studies.

Patients with temporal lobe epilepsy (TLE) due to mesial temporal sclerosis (MTS) are eligible candidates for resective epilepsy surgery. We report on 2 male patients aged 4 years with suspected TLE due to MTS who were referred for presurgical evaluation. Both patients came to medical attention within the first year of life suffering from febrile status epileptici and subsequent unprovoked seizures. The following years, moderate developmental delay was present. High-resolution magnetic resonance imaging confirmed hippocampal sclerosis. Continuous EEG video monitoring revealed seizure patterns contralateral to the MTS in both patients. Genetic analysis was performed as both the clinical presentation of the patients and EEG video monitoring findings were not consistent with the presence of the hippocampal sclerosis alone and revealed de novo mutations within exon of the SCN1A gene. Resective surgical strategies were omitted due to the genetic findings. In conclusion, both patients suffered from a dual pathology syndrome with ( a) TLE related to MTS resulting most likely from recurrent febrile status in early childhood and ( b) Dravet syndrome, which is most likely the cause of the febrile convulsions leading to the MTS in these 2 patients.