Serotonin transporter gene × environment and risk of depression in community-treated epilepsy

Inhibitory Neurons in Nucleus Tractus Solitarius Are Involved in Decrease of Heart Rate Variability and Development of Depression-Like Behaviors in Temporal Lobe Epilepsy

BACKGROUND

Diminished heart rate variability (HRV) has been observed in epilepsy, especially in epilepsy with depressive disorders. However, the underlying mechanism remains elusive.

METHODS

We studied HRV, spontaneous recurrent seizures, and depression-like behaviors in different phases of pilocarpine-induced temporal lobe epilepsy (TLE) in mice. Single-cell RNA sequencing analysis was used to identify various nerve cell subsets in TLE mice with and without depression. Differentially expressed gene (DEG) analysis was performed in epilepsy, depression, and HRV central control-related brain areas.

RESULTS

We found decreased HRV parameters in TLE mice, and alterations were positively correlated with the severity of depression-like behaviors. The severity of depression-like behaviors was correlated with the frequency of spontaneous recurrent seizure. Characteristic expression of mitochondria-related genes was significantly elevated in mice with depression in glial cells, and the enrichment analysis of those DEGs showed an enriched GABAergic synapse pathway in the HRV central control-related brain area. Furthermore, inhibitory neurons in the nucleus tractus solitarius, which is an HRV central control-related brain area, were specifically expressed in TLE mice combined with depression compared with those in mice without depression. A significantly enriched long-term depression pathway in DEGs from inhibitory neurons was found.

CONCLUSIONS

Our study reported correlations between HRV and epilepsy-depression comorbidity in different phases of TLE. More importantly, we found that HRV central control-related inhibitory neurons are involved in the development of depression in TLE, providing new insights into epilepsy comorbid with depression.

Interictal Heart Rate Variability as a Biomarker for Comorbid Depressive Disorders among People with Epilepsy

Depressive disorders are common among people with epilepsy (PwE). We here aimed to report an unbiased automatic classification of epilepsy comorbid depressive disorder cases via training a linear support vector machine (SVM) model using the interictal heart rate variability (HRV) data. One hundred and eighty-six subjects participated in this study. Among all participants, we recorded demographic information, epilepsy states and neuropsychiatric features. For each subject, we performed simultaneous electrocardiography and electroencephalography recordings both in wakefulness and non-rapid eye movement (NREM) sleep stage. Using these data, we systematically explored the full parameter space in order to determine the most effective combinations of data to classify the depression status in PwE. PwE with depressive disorders exhibited significant alterations in HRV parameters, including decreased time domain and nonlinear domain values both in wakefulness and NREM sleep stage compared with without depressive disorders and non-epilepsy controls. Interestingly, PwE without depressive disorder showed the same level of HRV values as the non-epilepsy control subjects. The SVM classification model of PwE depression status achieved a higher classification accuracy with the combination of HRV parameters in wakefulness and NREM sleep stage. Furthermore, the receiver operating characteristic (ROC) curve of the SVM classification model showed a satisfying area under the ROC curve (AUC: 0.758). Intriguingly, we found that the HRV measurements during NREM sleep are particularly important for correct classification, suggesting a mechanistic link between the dysregulation of heart rate during sleep and the development of depressive disorders in PwE. Our classification model may provide an objective measurement to assess the depressive status in PwE.

Genetic polymorphisms of the serotonin transporter are not related with depression in temporal lobe epilepsy caused by hippocampal sclerosis

BACKGROUND

Mood disorders are the most frequent psychiatric disorders in patients with temporal lobe epilepsy caused by hippocampal sclerosis (TLE-HS). The pathophysiological mechanisms in common between TLE and mood disorders include abnormalities in the serotonergic pathway. We aimed to evaluate the association between serotonin transporter genetic polymorphisms - 5-HTTLPR and 5-HTTVNTR - and the presence of mood disorders in patients with TLE-HS.

METHODS

We evaluated 119 patients with TLE-HS, with and without psychiatric disorder; 146 patients diagnosed with major depressive disorder (MDD), and 113 healthy volunteers. Individuals were genotyped for the 5-HTTLPR and 5-HTTVNTR polymorphisms.

RESULTS

No difference was observed between the TLE-HS groups, healthy controls, and MDD without epilepsy. There was a correlation between the 12-allele of the 5-HTTVNTR and the family history of patients with epilepsy with TLE-HS (p = 0.013).

CONCLUSIONS

In this study conducted in two Brazilian centers, the serotonin transporter polymorphisms evaluated cannot be associated with depressive disorder in patients with TLE-HS. Still, they do have some influence over some clinical characteristics of epilepsy in TLE-HS. These data may not be reproduced in other populations with distinct ethnic characteristics.

Depression and Anxiety in the Epilepsies: from Bench to Bedside

PURPOSE OF REVIEW

Depression and anxiety substantially contribute to interictal disability in patients with epilepsy (PWE). This review summarizes current studies that shed light on mechanisms of comorbidity.

RECENT FINDINGS

Mounting epidemiological data implicate shared risk factors for anxiety/depression and seizure propensity, but these remain largely elusive and probably vary by epilepsy type. Within PWE, these symptoms appear to be associated with unique genetic, neuropathological, and connectivity profiles. Temporal lobe epilepsy has received enormous emphasis particularly in preclinical studies of comorbidity, where candidate neurobiological mechanisms underlying bidirectionality have been tested without psychopharmacological confounds. Depression and anxiety in epilepsy reflect dysfunction within broadly distributed limbic networks that may be the cause or consequence of epileptogenesis. In refractory epilepsy, seizures and/or certain anticonvulsants may distort central emotional homeostatic mechanisms that perpetually raise seizure risk. Developing future safe and effective combined anticonvulsant-antidepressant treatments will require a detailed understanding of anatomical and molecular nodes that pleiotropically enhance seizure risk and negatively alter emotionality.

Genetic polymorphisms of the 5HT receptors are not related with depression in temporal lobe epilepsy caused by hippocampal sclerosis

BACKGROUND

Temporal lobe epilepsy caused by hippocampal sclerosis (TLE-HS) is the most frequent form of drug-resistant epilepsy in adults. Mood disorders are the most frequent psychiatric comorbidities observed in these patients. Common pathophysiological mechanisms of epilepsy and psychiatric comorbidities include abnormalities in the serotonin pathway. The primary goal of this study was to determine the possible association between polymorphisms of genes encoding the serotonin receptors 5HT1A (rs6295), 5HT1B (rs6296), and 5HT2C (rs6318) and the presence of mood disorders in patients with TLE-HS. Our secondary goal was to evaluate the possible association between these variants and susceptibility to develop seizures in TLE-HS.

METHODS

We assessed 119 patients with TLE-HS, with and without psychiatric comorbidities; 146 patients with major depressive disorder; and 113 healthy volunteers. Individuals were genotyped for the rs6295, rs6296, and rs6318 polymorphisms.

RESULTS

No difference was observed between the group with TLE-HS, healthy controls, and the group with major depressive disorder without epilepsy regarding the polymorphisms that were evaluated. There was no correlation between rs6318, rs6295, rs6296, and epilepsy-related factors and history of psychiatric comorbidities.

CONCLUSIONS

Our work suggests that the studied polymorphisms were not related to the presence of TLE, psychiatric comorbidities in TLE, and epilepsy-related factors.

Gene-environment interactions between stress and 5-HTTLPR in depression: A meta-analytic update

BACKGROUND

Meta-analyses have yielded contradictory findings concerning the role of 5-HTTLPR in interaction with stress (GxE) in depression. The current meta-analysis investigates if these contradictory findings are a result of differences between studies in methodological approaches towards the assessment of stress and depression.

METHODS

After performing a systematic database search (February to December 2016), first, a meta-analysis was used to investigate the total effect size and publication bias. Second, stratified meta-analyses were used to investigate the potential moderating influence of different methodological approaches on heterogeneity of study findings. Third, a meta-regression was used to investigate the combined influence of the methodological approaches on the overall effect size.

RESULTS

Results showed a small but significant effect of 5-HTTLPR in interaction with stress in the prediction of depression (OR[95%CI] = 1.18[1.09; 1.28], n = 48 effect sizes from 51 studies, totaling 51,449 participants). There was no evidence of publication bias. Heterogeneity of effect sizes was a result of outliers and not due to different methodological approaches towards the assessment of stress and depression. Yet, there was some evidence that studies adopting a categorical and interview approach to the assessment of stress report higher GxE effects, but further replication of this finding is needed.

LIMITATIONS

A large amount of heterogeneity (i.e., 46%) was not explained by the methodological factors included in the study and there was a low response rate of invited studies.

CONCLUSIONS

The current meta-analysis provides new evidence for the robustness of the interaction between stress and 5-HTTLPR in depression.

Single-Gene Determinants of Epilepsy Comorbidity

Common somatic conditions are bound to occur by chance in individuals with neurological disorders as prevalent as epilepsy, but when biological links underlying the comorbidity can be uncovered, the relationship may provide clues into the origin and mechanisms of both. The expanding list of monogenic epilepsies and their associated clinical features offer a remarkable opportunity to mine the epilepsy genome for coordinate neurodevelopmental phenotypes and examine their pathogenic mechanisms. Defined single-gene-linked epilepsy syndromes identified to date include all of the most frequently cited comorbidities, such as cognitive disorders, autism, migraine, mood disorders, late-onset dementia, and even premature lethality. Gene-linked comorbidities may be aggravated by, or independent of, seizure history. Mutations in these genes establish clear biological links between abnormal neuronal synchronization and a variety of neurobehavioral disorders, and critically substantiate the definition of epilepsy as a complex spectrum disorder. Mapping the neural circuitry of epilepsy comorbidities and understanding their single-gene risk should substantially clarify this challenging aspect of clinical epilepsy management.

Risk factors for depression in community-treated epilepsy: systematic review

OBJECTIVE

Depression is one of the most common psychiatric comorbidities in epilepsy; however, the factors contributing to this association remain unclear. There is a growing consensus that methodological limitations, particularly selection bias, affect many of the original studies. A systematic review focussed on community-based studies offers an alternative approach for the identification of the risk factors for depression.

METHODS

Searches were performed in MEDLINE (Ovid), 2000 to 31 December 2013, EMBASE, and Google Scholar to identify studies examining risk factors for depression in epilepsy. Community-based studies of adults with epilepsy that reported at least one risk factor for depression were included.

RESULTS

The search identified 17 studies that met selection criteria, representing a combined total of 12,212 people with epilepsy with a mean sample size of 718. The most consistent risk factors for depression were sociodemographic factors, despite the fact that most studies focus on epilepsy-related factors.

SIGNIFICANCE

Most studies lacked a systematic conceptual approach to investigating depression, and few risk factors were consistently well studied. Future community-based studies require a detailed systematic approach to improve the ability to detect risk factors for depression in epilepsy. Psychological factors were rarely studied in community-based samples with epilepsy, although the consistent association with depression in the few studies that did suggests this warrants further examination.