Do mood instability symptoms in epilepsy represent formal bipolar disorder?

Abnormal patterns of sleep and waking behaviors are accompanied by neocortical oscillation disturbances in an Ank3 mouse model of epilepsy-bipolar disorder comorbidity

ANK3 is a leading bipolar disorder (BD) candidate gene in humans and provides a unique opportunity for studying epilepsy-BD comorbidity. Previous studies showed that deletion of Ank3-1b, a BD-associated variant of Ank3 in mice leads to increased firing threshold and diminished action potential dynamic range of parvalbumin (PV) interneurons and absence epilepsy, thus providing a biological mechanism linking epilepsy and BD. To explore the behavioral overlap of these disorders, we characterized behavioral patterns of Ank3-1b KO mice during overnight home-cage activity and examined network activity during these behaviors using paired video and EEG recordings. Since PV interneurons contribute to the generation of high-frequency gamma oscillations, we anticipated changes in the power of neocortical EEG signals in the gamma frequency range (> 25 Hz) during behavioral states related to human BD symptoms, including abnormal sleep, hyperactivity, and repetitive behaviors. Ank3-1b KO mice exhibited an overall increase in slow gamma (~25-45 Hz) power compared to controls, and slow gamma power correlated with seizure phenotype severity across behaviors. During sleep, increased slow gamma power correlated with decreased time spent in the rapid eye movement (REM) stage of sleep. Seizures were more common during REM sleep compared to non-REM (NREM) sleep. We also found that Ank3-1b KO mice were hyperactive and exhibited a repetitive behavior phenotype that co-occurred with increased slow gamma power. Our results identify a novel EEG biomarker associating Ank3 genetic variation with BD and epilepsy and suggest modulation of gamma oscillations as a potential therapeutic target.

Prevalence of Bipolar Symptoms or Disorder in Epilepsy: A Systematic Review and Meta-Analysis

BACKGROUND AND OBJECTIVES

This systematic review with meta-analysis (PROSPERO: CRD42021249336) was performed to estimate the pooled lifetime prevalence of bipolar symptoms (BS) and bipolar disorder (BD) in people with epilepsy (PWE).

METHODS

A search was performed on June 5^th, 2021, in four databases (MEDLINE/PubMed, Ovid EMBASE, Ovid APA PsycInfo, and Web of Science) for original research reporting on BS/BD in PWE, with no restriction on language or time of publication. Inclusion criteria were as follows: 1) original research, 2) cross-sectional study design component, 3) reported a lifetime prevalence of BS/BD or enough information to calculate an estimate, and 4) reported the method by which participants were deemed bipolar. Studies based on an exclusively pediatric population were excluded. To calculate pooled lifetime prevalence of BS/BD, two meta-analytic random-effects models were fitted, one for BS, and the other for BD. Risk of bias was assessed using a standardized appraisal tool for studies reporting prevalence. Certainty of evidence was evaluated using the GRADE approach.

RESULTS

A total of 750 records were screened, and 17 studies were included for analysis: seven provided prevalence estimates for only BS, eight for only BD, and two for both BS and BD. After outlier exclusion and subgroup analysis using screening method as a moderator, the pooled prevalence of BS in PWE was 12.3% [95% CI; 10.6-14.1%] (7,506 PWE). The pooled prevalence of BD in PWE was 4.5% [95% CI; 2.2-7.4%] (48,334 PWE). Considerable heterogeneity was present - more so for BD than for BS - and could be explained through differences in population demographics and study methodology.

DISCUSSION

This study's main limitation was regarding the certainty of evidence. Notwithstanding, our estimates of prevalence should prompt further research on BS/BD in PWE. Given the significant morbidity associated to BD, clinicians should carefully screen PWE for BS.

Insomnia moderates the association between recurrent seizures and emotional instability in persons with epilepsy

PURPOSE

We investigated the moderating effect of sleep disturbance on the association between seizure recurrence and emotional instability in patients with epilepsy, independent of psychological distress.

METHODS

This was a cross-sectional study. Patients completed the short form of the Affective Lability Scale (ALS-18), Insomnia Severity Index (ISI), Patient Health Questionnaire-9 (PHQ-9), and Generalized Anxiety Disorder-7 (GAD-7). A stepwise linear regression analysis and an analysis of covariance with an interaction term were performed.

RESULTS

A total of 171 subjects (63.2% men) were included. The mean ALS-18 score was 15.6 ± 11.3. An ISI ≥ 15, PHQ-9 ≥ 10, and GAD-7 ≥ 7 were noted in 20.5%, 18.1%, and 23.4% of subjects, respectively. A stepwise linear regression analysis found that recurrent seizures in the last year, an ISI ≥ 15, a GAD-7 ≥ 7, and use of levetiracetam were significant and independent factors that were positively associated with higher ALS-18 scores. The coefficient of determination for the model was 0.331. The interaction between recurrent seizures and an ISI ≥ 15 had a significant effect on the ALS-18 scores (F = 6.812, p = 0.010, partial eta² = 0.040). An ISI ≥ 15 was associated with ALS-18 scores in patients without seizure recurrence (p < 0.001). This association almost reached significance (p = 0.084) in those with recurrent seizures. In contrast, the presence of recurrent seizures was associated with ALS-18 scores in patients with an ISI < 15 (p < 0.001), but not in those with an ISI ≥ 15 (p = 0.360).

CONCLUSIONS

The significant interaction between insomnia and seizure status may have an effect on emotional instability. These findings have clinical implications in the development of potential interventions for emotional instability in patients with epilepsy.

Hippocampal Pathophysiology: Commonality Shared by Temporal Lobe Epilepsy and Psychiatric Disorders

Accumulating evidence points to the association of epilepsy, particularly, temporal lobe epilepsy (TLE), with psychiatric disorders, such as schizophrenia. Among these illnesses, the hippocampus is considered the regional focal point of the brain, playing an important role in cognition, psychosis, and seizure activity and potentially suggesting common etiologies and pathophysiology of TLE and schizophrenia. In the present review, we overview abnormal network connectivity between the dentate gyrus (DG) and the Cornus Ammonis area 3 (CA3) subregions of the hippocampus relative to the induction of epilepsy and schizophrenia. In light of our recent finding on the misguidance of hippocampal mossy fiber projection in the rodent model of schizophrenia, we discuss whether ectopic mossy fiber projection is a commonality in order to evoke TLE as well as symptoms related to schizophrenia.

Ankyrin-G isoform imbalance and interneuronopathy link epilepsy and bipolar disorder

ANK3, encoding the adaptor protein Ankyrin-G (AnkG), has been implicated in bipolar disorder by genome-wide association studies. ANK3 has multiple alternative first exons, and a bipolar disorder-associated ANK3 variant has been shown to reduce the expression of exon 1b. Here we identify mechanisms through which reduced ANK3 exon 1b isoform expression disrupts neuronal excitation-inhibition balance. We find that parvalbumin (PV) interneurons and principal cells differentially express ANK3 first exon subtypes. PV interneurons express only isoforms containing exon 1b, whereas excitatory principal cells express exon 1e alone or both 1e and 1b. In transgenic mice deficient for exon 1b, PV interneurons lack voltage-gated sodium channels at their axonal initial segments and have increased firing thresholds and diminished action potential dynamic range. These mice exhibit an Ank3 gene dosage-dependent phenotype including behavior changes modeling bipolar disorder, epilepsy and sudden death. Thus ANK3's important association with human bipolar susceptibility may arise from imbalance between AnkG function in interneurons and principal cells and resultant excessive circuit sensitivity and output. AnkG isoform imbalance is a novel molecular endophenotype and potential therapeutic target.

Voltage-gated sodium channel β subunits: The power outside the pore in brain development and disease

Voltage gated sodium channels (VGSCs) were first identified in terms of their role in the upstroke of the action potential. The underlying proteins were later identified as saxitoxin and scorpion toxin receptors consisting of α and β subunits. We now know that VGSCs are heterotrimeric complexes consisting of a single pore forming α subunit joined by two β subunits; a noncovalently linked β1 or β3 and a covalently linked β2 or β4 subunit. VGSC α subunits contain all the machinery necessary for channel cell surface expression, ion conduction, voltage sensing, gating, and inactivation, in one central, polytopic, transmembrane protein. VGSC β subunits are more than simple accessories to α subunits. In the more than two decades since the original cloning of β1, our knowledge of their roles in physiology and pathophysiology has expanded immensely. VGSC β subunits are multifunctional. They confer unique gating mechanisms, regulate cellular excitability, affect brain development, confer distinct channel pharmacology, and have functions that are independent of the α subunits. The vast array of functions of these proteins stems from their special station in the channelome: being the only known constituents that are cell adhesion and intra/extracellular signaling molecules in addition to being part of channel complexes. This functional trifecta and how it goes awry demonstrates the power outside the pore in ion channel signaling complexes, broadening the term channelopathy beyond defects in ion conduction. This article is part of the Special Issue entitled 'Channelopathies.'

Epilepsy and bipolar disorder

It is well recognized that mood disorders and epilepsy commonly co-occur. Despite this, our knowledge regarding the relationship between epilepsy and bipolar disorder is limited. Several shared features between the two disorders, such as their episodic nature and potential to run a chronic course, and the efficacy of some antiepileptic medications in the prophylaxis of both disorders, are often cited as evidence of possible shared underlying pathophysiology. The present paper aims to review the bidirectional associations between epilepsy and bipolar disorder, with a focus on epidemiological links, evidence for shared etiology, and the impact of these disorders on both the individual and wider society. Better recognition and understanding of these two complex disorders, along with an integrated clinical approach, are crucial for improved evaluation and management of comorbid epilepsy and mood disorders.

Does Mood Disorder Questionnaire identify sub-threshold bipolarity? Evidence studying worsening of quality of life

OBJECTIVE

It is debated whether the Mood Disorder Questionnaire (MDQ) can generate false positives by screening other disorders as bipolar, or identify sub-threshold bipolarity. The aim is to verify if Quality of Life (QoL) impairment in MQD positives in the community is due to MDQ positivity itself, or to psychiatric diagnosis associated with MDQ positivity (supporting the former hypothesis).

METHOD

Community survey. Sample randomized after stratification of the adult population in the records of seven Italian regions.

TOOLS

MDQ; Short Form Health Survey (SF-12); semi-structured clinical interview carried out by clinicians.

RESULTS

Positives at MDQ show worsening QoL with an attributable burden of 2.8 ± 1.8 lower than in MDD (5.6 ± 3.6, p < 0.001) or Eating Disorders (4.4 ± 6.6, p < 0.03) and similar to Panic Disorder (2.9 ± 0.9, p = 0.44). The burden is lower in the middle-aged (25-59 years) than in the young (18-24) (4.65 ± 4.5 vs 2.58 ± 2.0, p=0.007) or in the elderly (≥60) (4.12 ± 3.2; p = 0.024). In the elderly the burden is independent from comorbid psychiatric disorders.

LIMITATIONS

This is a preliminary study based on one survey not designed to test this specific hypothesis, thus its results have a heuristic value only.

CONCLUSIONS

The worsening of QoL due to positivity at MDQ is largely independent from comorbid conditions, supporting the hypothesis that MDQ positivity identifies a specific area of suffering that is "subthreshold" to the psychiatric diagnosis, and relevant for public health.

The immature dentate gyrus represents a shared phenotype of mouse models of epilepsy and psychiatric disease

OBJECTIVES

There is accumulating evidence to suggest psychiatric disorders, such as bipolar disorder and schizophrenia, share common etiologies, pathophysiologies, genetics, and drug responses with many of the epilepsies. Here, we explored overlaps in cellular/molecular, electrophysiological, and behavioral phenotypes between putative mouse models of bipolar disorder/schizophrenia and epilepsy. We tested the hypothesis that an immature dentate gyrus (iDG), whose association with psychosis in patients has recently been reported, represents a common phenotype of both diseases.

METHODS

Behaviors of calcium/calmodulin-dependent protein kinase II alpha (α-CaMKII) heterozygous knock-out (KO) mice, which are a representative bipolar disorder/schizophrenia model displaying iDG, and pilocarpine-treated mice, which are a representative epilepsy model, were tested followed by quantitative polymerase chain reaction (qPCR)/immunohistochemistry for mRNA/protein expression associated with an iDG phenotype. In vitro electrophysiology of dentate gyrus granule cells (DG GCs) was examined in pilocarpine-treated epileptic mice.

RESULTS

The two disease models demonstrated similar behavioral deficits, such as hyperactivity, poor working memory performance, and social withdrawal. Significant reductions in mRNA expression and immunoreactivity of the mature neuronal marker calbindin and concomitant increases in mRNA expression and immunoreactivity of the immature neuronal marker calretinin represent iDG signatures that are present in both mice models. Electrophysiologically, we have confirmed that DG GCs from pilocarpine-treated mice represent an immature state. A significant decrease in hippocampal α-CaMKII protein levels was also found in both models.

CONCLUSIONS

Our data have shown iDG signatures from mouse models of both bipolar disorder/schizophrenia and epilepsy. The evidence suggests that the iDG may, in part, be responsible for the abnormal behavioral phenotype, and that the underlying pathophysiologies in epilepsy and bipolar disorder/schizophrenia are strikingly similar.