Kjell Heuser

Common genetic variation and susceptibility to partial epilepsies: a genome-wide association study

Partial epilepsies have a substantial heritability. However, the actual genetic causes are largely unknown. In contrast to many other common diseases for which genetic association-studies have successfully revealed common variants associated with disease risk, the role of common variation in partial epilepsies has not yet been explored in a well-powered study. We undertook a genome-wide association-study to identify common variants which influence risk for epilepsy shared amongst partial epilepsy syndromes, in 3445 patients and 6935 controls of European ancestry. We did not identify any genome-wide significant association. A few single nucleotide polymorphisms may warrant further investigation. We exclude common genetic variants with effect sizes above a modest 1.3 odds ratio for a single variant as contributors to genetic susceptibility shared across the partial epilepsies. We show that, at best, common genetic variation can only have a modest role in predisposition to the partial epilepsies when considered across syndromes in Europeans. The genetic architecture of the partial epilepsies is likely to be very complex, reflecting genotypic and phenotypic heterogeneity. Larger meta-analyses are required to identify variants of smaller effect sizes (odds ratio <1.3) or syndrome-specific variants. Further, our results suggest research efforts should also be directed towards identifying the multiple rare variants likely to account for at least part of the heritability of the partial epilepsies. Data emerging from genome-wide association-studies will be valuable during the next serious challenge of interpreting all the genetic variation emerging from whole-genome sequencing studies.

Variants of the genes encoding AQP4 and Kir4.1 are associated with subgroups of patients with temporal lobe epilepsy

OBJECTIVE The etiopathogenesis of temporal lobe epilepsy (TLE) and its subgroups - mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) and TLE with antecedent febrile seizures (TLE-FS) - is poorly understood. It has been proposed that the water channel aquaporin-4 (AQP4) and the potassium channel Kir4.1 (KCNJ10 gene) act in concert to regulate extracellular K(+) homeostasis and that functional alterations of these channels influence neuronal excitability. The current study was designed to identify variants of the AQP4 and KCNJ10 genes associated with TLE and subgroups of this condition. MATERIAL AND METHODS We included 218 Norwegian patients with TLE and 181 ethnically matched healthy controls. An association study was established in which all TLE patients were compared with healthy controls. Additionally, subgroups of 56 MTLE-HS patients were compared with 162 TLE patients without HS, and 102 TLE-FS patients were compared with 105 TLE without FS. RESULTS We found eight single SNPs, seven in KCNJ10 and one between KCNJ10 and KCNJ9, associated with TLE-FS (nominal p-values from 0.009 to 0.041). Seven of the SNPs segregate into one large haplotype block expanding from KCNJ10 to KCNJ9, including the region interposed those genes. One haplotype was overrepresented in the TLE-FS cases (nominal p-value 0.014). These results were confirmed by explorative multivariate analysis indicating that a combination of SNPs from KCNJ10, the region between KCNJ10 and KCNJ9, and the AQP4 gene is associated with TLE-FS. For the TLE cohort as a whole, explorative multivariate analysis indicated a combination of SNPs from the KCNJ10 and AQP4 genes in association with TLE. CONCLUSION Variations in the AQP4 and the KCNJ10/KCNJ9 region are likely to be associated with TLE, particularly TLE-FS, supporting the suggestion that perturbations of water and K(+) transport are involved in the etiopathogenesis of TLE.

Loss of Perivascular Kir4.1 Potassium Channels in the Sclerotic Hippocampus of Patients With Mesial Temporal Lobe Epilepsy

Abstract Recent experimental data in mice have shown that the inwardly rectifying K+ channel Kir4.1 mediates K+ spatial buffering in the hippocampus. Here we used immunohistochemistry to examine the distribution of Kir4.1 in hippocampi from patients with medication-refractory temporal lobe epilepsy. The selectivity of the antibody was confirmed in mice with a glial conditional deletion of the gene encoding Kir4.1. These mice showed a complete loss of labeled cells, indicating that Kir4.1 is restricted to glia. In human cases, Kir4.1 immunoreactivity observed in cells morphologically consistent with astrocytes was significantly reduced in 12 patients with hippocampal sclerosis versus 11 patients without sclerosis and 4 normal autopsy controls. Loss of astrocytic Kir4.1 immunoreactivity was most pronounced around vessels and was restricted to gliotic areas. Loss of Kir4.1 expression was associated with loss of dystrophin and &agr;-syntrophin, but not with loss of &bgr;-dystroglycan, suggesting partial disruption of the dystrophin-associated protein complex. The changes identified in patients with hippocampal sclerosis likely interfere with K+ homeostasis and may contribute to the epileptogenicity of the sclerotic hippocampus.

Microvascular decompression for hemifacial spasm: postoperative neurologic follow‐up and evaluation of life quality

Microvascular decompression (MVD) is an effective and safe treatment in hemifacial spasm (HFS). Postoperative evaluations are usually made by neurosurgeons. Follow‐up studies performed by neurologists and postoperative quality of life (QoL) investigations are lacking. All 25 HFS patients operated with MVD in our centre between 2000 and 2004 were evaluated with the recently validated HFS‐7 scheme, extended with the item ’sleep disturbance due to HFS’ (HFS‐8). The patients underwent a careful neurological examination median 3 years after the operation. The evaluation focused on clinical aspects, changes in blood pressure and time until observable effect of MVD. The evaluation of HFS‐7 questionnaire and the extended form (HFS‐8) showed significant improvement in QoL after MVD. Neurological outcome was in almost all cases excellent or good. Eleven (44%) patients had no neurological deficits at all. Only one patient had serious complications with ipsilateral facial palsy, deafness, balance problems and vertigo. The other patients had minor neurological findings or symptoms. Eighteen (72%) patients experienced early effect within 3 months after MVD; seven (28%) patients had late effect between 6 and 14 months. Median age of the patients with late effect (62.6 years) was significantly higher than in those with early effect (52.7 years).

Redistribution of monocarboxylate transporter 2 on the surface of astrocytes in the human epileptogenic hippocampus.

Emerging evidence points to monocarboxylates as key players in the pathophysiology of temporal lobe epilepsy (TLE) with hippocampal sclerosis (mesial temporal lobe epilepsy, MTLE). Monocarboxylate transporters (MCTs) 1 and 2, which are abundantly present on brain endothelial cells and perivascular astrocyte endfeet, respectively, facilitate the transport of monocarboxylates and protons across cell membranes. Recently, we reported that the density of MCT1 protein is reduced on endothelial cells and increased on astrocyte plasma membranes in the hippocampal formation in patients with MTLE and in several animal models of the disorder. Because the perivascular astrocyte endfeet comprise an important part of the neurovascular unit, we now assessed the distribution of the MCT2 in hippocampal formations in TLE patients with (MTLE) or without hippocampal sclerosis (non‐MTLE). Light microscopic immunohistochemistry revealed significantly less perivascular MCT2 immunoreactivity in the hippocampal formation in MTLE (n = 6) than in non‐MTLE (n = 6) patients, and to a lesser degree in non‐MTLE than in nonepilepsy patients (n = 4). Immunogold electron microscopy indicated that the loss of MCT2 protein occurred on perivascular astrocyte endfeet. Interestingly, the loss of MCT2 on astrocyte endfeet in MTLE (n = 3) was accompanied by an upregulation of the protein on astrocyte membranes facing synapses in the neuropil, when compared with non‐MTLE (n = 3). We propose that the altered distribution of MCT1 and MCT2 in TLE (especially MTLE) limits the flux of monocarboxylates across the blood–brain barrier and enhances the exchange of monocarboxylates within the brain parenchyma.

Is the brain water channel aquaporin‐4 a pathogenetic factor in idiopathic intracranial hypertension? Results from a combined clinical and genetic study in a Norwegian cohort

Purpose:  Idiopathic intracranial hypertension (IIH) is a condition of increased intracranial pressure of unknown aetiology. Patients with IIH usually suffer from headache and visual disturbances. High intracranial pressure despite normal ventricle size and negative MRI indicate perturbed water flux across cellular membranes, which is provided by the brain water channel aquaporin‐4 (AQP4). IIH could be associated with malfunctioning intracerebral water homeostasis and cerebrospinal fluid (CSF) reabsorption based on functional or regulatory alterations of AQP4.

Overnight response to infliximab in neurosarcoidosis: a case report and review of infliximab treatment practice.

ObjectivesCentral nervous system manifestations of sarcoidosis occur in approximately 5% of patients with sarcoidosis, often lead to substantial morbidity, and therefore require immediate treatment. Spinal cord involvement is exceptionally rare. The tumor necrosis factor-&agr; inhibitor infliximab seems to be an effective alternative in severe cases, refractory to other therapies, but a standard concept of treatment is lacking. MethodsWe presented a case of severe corticosteroid-refractory spinal cord sarcoidosis with immediate and dramatic response to infliximab. In addition, we reviewed the literature on infliximab therapy in neurosarcoidosis and drew parallels to other medical fields in order to have a basis for decision making in the initiation and discontinuation of treatment. ResultsWe identified a total of 34 case reports on effective infliximab treatment of therapy-resistant neurosarcoidosis through PubMed search. Nineteen of the 34 cases reported the duration until treatment response. In accordance with our patient, 14 of the 34 case reports showed improvement between first and third infusion. Eight of the 34 cases reported sustained remission after cessation of infliximab. No definite treatment regimen was used. ConclusionsInfliximab seems to be a fast-acting and effective drug for severe neurosarcoidosis. No systematic treatment strategy is available because of lack of controlled trials. Until then, therapy regimens may be adapted to those used in other medical fields where infliximab treatment is well established.

Is Temporal Lobe Epilepsy with childhood febrile seizures a distinctive entity? A comparative study

OBJECTIVE Pharmacoresistance continues to be a major challenge in Temporal Lobe Epilepsies (TLE). A key to overcome pharmacoresistance is to identify subgroups among the TLE and disclose their specific molecular pathways. This will facilitate a tailored pharmacological treatment and improve outcome. There is growing evidence in favor of the theory that TLE with childhood febrile seizures (TLE-FS) may represent one distinctive subgroup among the TLE. MATERIAL AND METHODS We compared clinical features from 102 TLE-FS patients with 105 TLE patients without FS. We also conducted a logistic regression analysis to adjust for possible confounders caused by overrepresentation of patients with Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis (MTLE-HS) in the TLE-FS group. RESULTS MTLE-HS was overrepresented in patients with TLE-FS (p=0.043). Age at epilepsy onset was lower in patients with TLE-FS (p<0.001). TLE-FS patients had a higher frequency of first grade family members with FS (p=0.003, adjusted for MTLE-HS: p=0.002). They were more frequently plagued with simple partial seizures (p=0.015, adjusted: p=0.038), and especially with vertiginous symptoms (p=0.004 adjusted: p=0.006). They also had the higher frequency of autonomic symptoms (p=0.003; adjusted: p=0.012), and more generalized tonic-clonic seizures (0.034; adjusted p=0.038). CONCLUSION We identified TLE-FS as a phenotype that can be delineated from other TLE. None of the characteristics are specific, but we disclosed a set of features also when adjusted for MTLE-HS.

Temporal lobe epilepsy and matrix metalloproteinase 9: a tempting relation but negative genetic association.

OBJECTIVE Neuroplasticity can be defined as the ability of the brain to adapt to environmental impacts. These adaptations include synapse formation and elimination, cortical reorganization, and neurogenesis. In epilepsy these mechanisms may become detrimental and contribute to disease progression. It has been proposed that Matrix Metalloproteinase 9 (MMP-9), a proteinase that cleaves extracellular matrix molecules, may be critically involved in aberrant synaptic formation in hippocampi of patients with Temporal Lobe Epilepsy (TLE). Here we present a case-control study designed to identify possible variants of the MMP-9 gene associated with human TLE. MATERIAL AND METHODS 218 Norwegian patients with TLE and 181 ethnically matched controls were compared in our association analysis. We also studied associations within two subgroups of TLE--Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis (MTLE-HS), and Temporal Lobe Epilepsy with childhood Febrile Seizures (TLE-FS). Single nucleotide polymorphisms (SNPs) were selected from HapMap and dbSNP databases for the MMP-9 gene on chromosome 20. We used standard haplotype analysis and multivariate explorative analysis. RESULTS There were no statistically significant associations between the analyzed SNPs in the MMP-9 gene and TLE, nor were any significant associations found with the two examined subgroups MTLE-HS and TLE-FS, confirmed by both analyses. CONCLUSION We could not identify any polymorphisms of the human MMP-9 gene that were associated with TLE, MTLE-HS or TLE-FS, in the selected SNPs. However, factors that influence MMP-9 gene expression, post-transcriptional modifications, or the balance between activation and inhibition of MMP-9 may play a role in the pathogenesis of TLE and other epileptic syndromes.

Identification of Srp9 as a febrile seizure susceptibility gene

Febrile seizures (FS) are the most common seizure type in young children. Complex FS are a risk factor for mesial temporal lobe epilepsy (mTLE). To identify new FS susceptibility genes we used a forward genetic strategy in mice and subsequently analyzed candidate genes in humans.