Tryptophan hydroxylase 2 (TPH2) gene polymorphisms and psychiatric comorbidities in temporal lobe epilepsy

TPH2-703 G/T polymorphism is associated with stress, depression, and psychosocial symptoms in mentally healthy Mexicans

Tryptophan hydroxylase (TPH) catalyzes the rate-limiting step of serotonin synthesis. TPH2 is the brain-specific isoform of this enzyme, and genetic variations in the TPH2 gene have been shown to impact its transcription and enzymatic activity and are associated with mood disorders. In this study we focused on the rs4570625 (-703G/T) single nucleotide polymorphism of TPH2 gene. By using conventional polymerase chain reaction (PCR), we examined the effect of this polymorphism on stress, anxiety, and depression symptoms as well as quality of life, evaluated based on the Holmes-Rahe Inventory, the Beck Anxiety Inventory, the Beck Depression Inventory, and the World Health Organization Quality of Life - Short Version, respectively. We found that individuals with the homozygous recessive T/T genotype had lower stress and depression scores. In addition, the quality of life in the psychological health domain was better in males with the T/T genotype. These results suggest that T/T genotype could decrease the susceptibility to developing stress and depression in the Mexican population without a diagnosis for an emotional disorder.

The Role of C1473G Polymorphism in Mouse Triptophan Hydroxylase 2 Gene in the Acute Effects of Ethanol on the c-fos Gene Expression and Metabolism of Biogenic Amines in the Brain

Tryptophan hydroxylase 2 is a key enzyme in the synthesis of the neurotransmitter serotonin, which plays an important role in the regulation of behavior and various physiological functions. We studied the effect of acute ethanol administration on the expression of the early response c-fos gene and metabolism of serotonin and catecholamines in the brain structures of B6-1473C and B6-1473G congenic mouse strains differing in the single-nucleotide substitution C1473G in the Tph2 gene and activity of the encoded enzyme. Acute alcoholization led to a significant upregulation of the c-fos gene expression in the frontal cortex and striatum of B6-1473G mice and in the hippocampus of B6-1473C mice and caused a decrease in the index of serotonin metabolism in the nucleus accumbens in B6-1473C mice and in the hippocampus and striatum of B6-1473G mice, as well as to the decrease in the norepinephrine level in the hypothalamus of B6-1473C mice. Therefore, the C1473G polymorphism in the Tph2 gene has a significant effect of acute ethanol administration on the c-fos expression pattern and metabolism of biogenic amines in the mouse brain.

Methylation of BDNF and SLC6A4 Gene Promoters in Brazilian Patients With Temporal Lobe Epilepsy Presenting or Not Psychiatric Comorbidities

The relationship between epilepsy and psychiatric comorbidities has been recognized for centuries, but its pathophysiological mechanisms are still misunderstood. It is biologically plausible that genetic or epigenetic variations in genes that codify important neurotransmitters involved in epilepsy as well as in psychiatric disorders may influence the development of the latter in patients with epilepsy. However, this possibility remains poorly investigated. The aim of this study was to evaluate the methylation profile of the BDNF and SLC6A4, two genes importantly involved in neuroplasticity, in patients with temporal lobe epilepsy (TLE) regarding the development or not of psychiatric comorbidities. One hundred and thirty-nine patients with TLE, 90 females and 45 males, were included in the study. The mean age of patients was 44.0 (+12.0) years, and mean duration of epilepsy was 25.7 (+13.3) years. The Structured Clinical Interview for DSM-IV shows that 83 patients (59.7%) had neuropsychiatric disorders and 56 (40.3%) showed no psychiatric comorbidity. Mood disorders were the most common psychiatric disorder observed, being present in 64 (46.0%) of all 139 patients. Thirty-three (23.7%) patients showed anxiety disorders, 10 (7.2%) patients showed history of psychosis and 8 (5.8%) patients showed history of alcohol//drug abuse. Considering all 139 patients, 18 (12.9%) demonstrated methylation of the promoter region of both BDNF and SLC6A4 genes. A significant decreased methylation profile was observed only in TLE patients with mood disorders when compared with TLE patients without a history of mood disorders (O.R. = 3.45; 95% C.I. = 1.08–11.11; p = 0.04). A sub-analysis showed that TLE patients with major depressive disorder mostly account for this result (O.R. = 7.20; 95% C.I. = 1.01–56.16; p = 0.042). A logistic regression analysis showed that the independent factors associated with a history of depression in our TLE patients was female sex (O.R. = 2.30; 95% C.I. = 1.02–5.18; p = 0.044), not controlled seizures (O.R. = 2.51; 95% C.I. = 1.16–5.41; p = 0.019) and decreased methylation in BDNF and SLC6A4 genes (O.R. = 5.32; 95% C.I. = 1.14–25.00; p = 0.033). Our results suggest that BDNF or SLC6A4 genes profile methylation is independently associated with depressive disorders in patients with epilepsy. Further studies are necessary to clarify these matters.

New Insights Into the Anticonvulsant Effects of Essential Oil From Melissa officinalis L. (Lemon Balm)

Melissa officinalis L. is used in traditional European and Iranian folk medicines to treat a plethora of neurological diseases including epilepsy. We utilized the in vitro and in vivo models of epilepsy to probe the anticonvulsant potentials of essential oil from M. officinalis (MO) to gain insight into the scientific basis for its applications in traditional medicine for the management of convulsive disorders. MO was evaluated for effects on maximal electroshock (MES) and pentylenetetrazole (PTZ) -induced seizures in mice, on 4–aminopyridine (4-AP)-brain slice model of epilepsy and sustained repetitive firing of current clamped neurons; and its ameliorative effects were examined on seizure severity, anxiety, depression, cognitive dysfunction, oxidative stress and neuronal cell loss in PTZ-kindled rats. MO reversibly blocked spontaneous ictal-like discharges in the 4-AP-brain slice model of epilepsy and secondary spikes from sustained repetitive firing, suggesting anticonvulsant effects and voltage-gated sodium channel blockade. MO protected mice from PTZ– and MES–induced seizures and mortality, and ameliorated seizure severity, fear-avoidance, depressive-like behavior, cognitive deficits, oxidative stress and neuronal cell loss in PTZ–kindled rats. The findings warrant further study for the potential use of MO and/or its constituent(s) as adjunctive therapy for epileptic patients.

Disturbance of phylogenetic layer-specific adaptation of human brain gene expression in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with typical neuropathological hallmarks, such as neuritic plaques and neurofibrillary tangles, preferentially found at layers III and V. The distribution of both hallmarks provides the basis for the staging of AD, following a hierarchical pattern throughout the cerebral cortex. To unravel the background of this layer-specific vulnerability, we evaluated differential gene expression of supragranular and infragranular layers and subcortical white matter in both healthy controls and AD patients. We identified AD-associated layer-specific differences involving protein-coding and non-coding sequences, most of those present in the subcortical white matter, thus indicating a critical role for long axons and oligodendrocytes in AD pathomechanism. In addition, GO analysis identified networks containing synaptic vesicle transport, vesicle exocytosis and regulation of neurotransmitter levels. Numerous AD-associated layer-specifically expressed genes were previously reported to undergo layer-specific switches in recent hominid brain evolution between layers V and III, i.e., those layers that are most vulnerable to AD pathology. Against the background of our previous finding of accelerated evolution of AD-specific gene expression, here we suggest a critical role in AD pathomechanism for this phylogenetic layer-specific adaptation of gene expression, which is most prominently seen in the white matter compartment.

Sex-dependent complex association of TPH2 with multiple dimensions of ADHD

BACKGROUND

Tryptophan hydroxylase 2 (TPH2) is a key enzyme in the biosynthesis of serotonin in the brain. This study aims to investigate the role of a functional variant in TPH2 (rs17110747) in the pathophysiology of ADHD. This variant has been implicated in mood disorders in recent meta-analysis. This study uses a comprehensive approach that combines association testing and pharmaco-dynamic evaluation of behaviour, in a large sample of children with ADHD (n = 570).

METHODS

The association between various ADHD relevant traits and rs17110747 was analyzed using family-based association tests (FBAT). Children were assessed by parents, teachers and research staff under three experimental conditions (EC): baseline, placebo, and methylphenidate using a double-blind placebo-controlled crossover trial.

OUTCOMES

FBAT analysis conducted in a sample stratified based on sex of the proband, showed that there was a highly significant overtransmission of the G allele from parents to affected girls. In addition, significant association with several behavioral and cognitive dimensions of ADHD was observed only when the proband was female. Further, girls with the G/G genotype (rs17110747) had greater response to placebo when evaluated by parents.

INTERPRETATION

These results suggest that there may be a complex association of TPH2 in the etiology of ADHD, with a sex-specific effect.

Serotonin and sudden unexpected death in epilepsy

Epilepsy is a highly prevalent disease characterized by recurrent, spontaneous seizures. Approximately one-third of epilepsy patients will not achieve seizure freedom with medical management and become refractory to conventional treatments. These patients are at greatest risk for sudden unexpected death in epilepsy (SUDEP). The exact etiology of SUDEP is unknown, but a combination of respiratory, cardiac, neuronal electrographic dysfunction, and arousal impairment is thought to underlie SUDEP. Serotonin (5-HT) is involved in regulation of breathing, sleep/wake states, arousal, and seizure modulation and has been implicated in the pathophysiology of SUDEP. This review explores the current state of understanding of the relationship between 5-HT, epilepsy, and respiratory and autonomic control processes relevant to SUDEP in epilepsy patients and in animal models.

Depressive, inflammatory, and metabolic factors associated with cognitive impairment in patients with epilepsy

PURPOSE

The purpose of this study was to examine the cognitive function and depressive traits most frequently associated with the clinical assessment of patients with epilepsy and if these clinical parameters are linked to glycolipid levels and inflammatory and apoptotic markers.

METHODS

Patients with epilepsy (n = 32) and healthy subjects (n = 41) were recruited to participate in this study. Neuropsychological evaluation was performed in both groups through a battery of cognitive tests. Inflammatory markers, apoptotic factors, and deoxyribonucleic acid (DNA) damage were measured in blood samples. Additionally, the metabolic markers total cholesterol (CHO), low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglyceride (TG), and glucose (GLU) levels were analyzed.

RESULTS

Statistical analyses showed that patients with epilepsy presented decreased scores in memory, attention, language, and executive function tests compared with the control group. Analysis revealed that there was negative correlation in epilepsy for seizure duration vs. oral language (R = -0.4484, p < 0.05) and seizure duration vs. problem solving (executive functions) (R = -0.3995, p < 0.05). This was also observed when comparing depression with temporal-spatial orientation (TSO) (R = -0.39, p < 0.05). Furthermore, we observed a higher depression score in patients with epilepsy than in the healthy ones. Statistical analyses showed higher acetylcholinesterase (AChE) (p < 0.05), interleukin 1β (IL-1β, p < 0.001), and tumor necrosis factor-alpha (TNF-α) (p < 0.001) levels compared with those in the control group. Moreover, patients with epilepsy had significantly higher serum levels of caspase 3 (CASP 3) (p < 0.001) and Picogreen (p < 0.001) compared with the control subjects. Regarding the metabolic markers, higher glycolipid levels were observed in the patients with epilepsy (CHO < 0.05*, LDL < 0.0001*, TG < 0.05*, GLU p < 0.05). High-density lipoprotein levels were not significant. The patients with epilepsy had significant correlation when comparing total language with TNF-α (R = -0.4, p < 0.05), praxes with CASP 3 (R = -0.52, p < 0.01), total CHO with total language (R = -0.48, p < 0.05), TG with semantic memory (R = -0.54, p < 0.05), TG with prospective memory (R = -0.2165, p < 0.02), TG with total memory (R = -0.53, p < 0.02), and GLU with total attention (R = -0.62, p < 0.002).

CONCLUSION

This study supports the evidence of a distinct neuropsychological profile between patients with epilepsy and healthy subjects. Furthermore, our findings suggest that inflammatory pathway, glycolipid profile, and depressive factors may be associated with cognitive dysfunction in patients with epilepsy.

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.

TPH2 polymorphisms across the spectrum of psychiatric morbidity: A systematic review and meta-analysis

Tryptophan hydroxylase 2 (TPH2) is the rate-limiting enzyme in brain serotonin synthesis. The TPH2 gene has frequently been investigated in relation to psychiatric morbidity. The aim of the present review is to integrate results from association studies between TPH2 single nucleotide polymorphisms (SNPs) and various psychiatric disorders, which we furthermore quantified with meta-analysis. We reviewed 166 studies investigating 69 TPH2 SNPs in a broad range of psychiatric disorders, including over 30,000 patients. According to our meta-analysis, TPH2 polymorphisms show strongest associations with mood disorders, suicide (attempt) and schizophrenia. Despite small effect sizes, we conclude that TPH2 SNPs in the coding and non-coding areas (rs4570625, rs11178997, rs11178998, rs10748185, rs1843809, rs4290270, rs17110747) are each associated with one or more psychopathological conditions. Our findings highlight the possible common serotonergic mechanisms of the investigated psychiatric disorders. Yet, the functional relevance of most TPH2 polymorphisms is unclear. Characterizing how exactly the different TPH2 variants influence the serotonergic neurotransmission is a next necessary step in understanding the psychiatric disorders where serotonin is implicated.

TPH-2 Polymorphisms Interact with Early Life Stress to Influence Response to Treatment with Antidepressant Drugs

BACKGROUND

Variation in genes implicated in monoamine neurotransmission may interact with environmental factors to influence antidepressant response. We aimed to determine how a range of single nucleotide polymorphisms in monoaminergic genes influence this response to treatment and how they interact with childhood trauma and recent life stress in a Chinese sample. An initial study of monoaminergic coding region single nucleotide polymorphisms identified significant associations of TPH2 and HTR1B single nucleotide polymorphisms with treatment response that showed interactions with childhood and recent life stress, respectively (Xu et al., 2012).

METHODS

A total of 47 further single nucleotide polymorphisms in 17 candidate monoaminergic genes were genotyped in 281 Chinese Han patients with major depressive disorder. Response to 6 weeks' antidepressant treatment was determined by change in the 17-item Hamilton Depression Rating Scale score, and previous stressful events were evaluated by the Life Events Scale and Childhood Trauma Questionnaire-Short Form.

RESULTS

Three TPH2 single nucleotide polymorphisms (rs11178998, rs7963717, and rs2171363) were significantly associated with antidepressant response in this Chinese sample, as was a haplotype in TPH2 (rs2171363 and rs1487278). One of these, rs2171363, showed a significant interaction with childhood adversity in its association with antidepressant response.

CONCLUSIONS

These findings provide further evidence that variation in TPH2 is associated with antidepressant response and may also interact with childhood trauma to influence outcome of antidepressant treatment.

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.

Susceptibility loci for heroin and cocaine addiction in the serotonergic and adrenergic pathways in populations of different ancestry

BACKGROUND

Drug addiction is influenced by genetic factors.

AIM

To determine if genetic variants in the serotonergic and adrenergic pathways are associated with heroin and/or cocaine addiction.

SUBJECTS & METHODS

The study examined 140 polymorphisms in 19 genes in 1855 subjects with predominantly European or African ancestries.

RESULTS

A total of 38 polymorphisms (13 genes) showed nominal associations, including novel associations in S100A10 (p11) and SLC18A2 (VMAT2). The association of HTR3B SNP rs11606194 with heroin addiction in the European ancestry subgroup remained significant after correction for multiple testing (p(corrected) = 0.04).

CONCLUSION

The study strengthens our previous findings of association of polymorphisms in HTR3A, HTR3B and ADRA1A. The study suggests partial overlap in genetic susceptibility between populations of different ancestry and between heroin and cocaine addiction.

Metabolic and mitochondrial disorders associated with epilepsy in children with autism spectrum disorder

Autism spectrum disorder (ASD) affects a significant number of individuals in the United States, with the prevalence continuing to grow. A significant proportion of individuals with ASD have comorbid medical conditions such as epilepsy. In fact, treatment-resistant epilepsy appears to have a higher prevalence in children with ASD than in children without ASD, suggesting that current antiepileptic treatments may be suboptimal in controlling seizures in many individuals with ASD. Many individuals with ASD also appear to have underlying metabolic conditions. Metabolic conditions such as mitochondrial disease and dysfunction and abnormalities in cerebral folate metabolism may affect a substantial number of children with ASD, while other metabolic conditions that have been associated with ASD such as disorders of creatine, cholesterol, pyridoxine, biotin, carnitine, γ-aminobutyric acid, purine, pyrimidine, and amino acid metabolism and urea cycle disorders have also been associated with ASD without the prevalence clearly known. Interestingly, all of these metabolic conditions have been associated with epilepsy in children with ASD. The identification and treatment of these disorders could improve the underlying metabolic derangements and potentially improve behavior and seizure frequency and/or severity in these individuals. This paper provides an overview of these metabolic disorders in the context of ASD and discusses their characteristics, diagnostic testing, and treatment with concentration on mitochondrial disorders. To this end, this paper aims to help optimize the diagnosis and treatment of children with ASD and epilepsy. This article is part of a Special Issue entitled "Autism and Epilepsy".