Sensory gating deficit is associated with catechol-O-methyltransferase polymorphisms in bipolar disorder

Cataloging the potential SNPs (single nucleotide polymorphisms) associated with quantitative traits, viz. BMI (body mass index), IQ (intelligence quotient) and BP (blood pressure): an updated review

Background

Single nucleotide polymorphism (SNP) variants are abundant, persistent and widely distributed across the genome and are frequently linked to the development of genetic diseases. Identifying SNPs that underpin complex diseases can aid scientists in the discovery of disease-related genes by allowing for early detection, effective medication and eventually disease prevention.

Main body

Various SNP or polymorphism-based studies were used to categorize different SNPs potentially related to three quantitative traits: body mass index (BMI), intelligence quotient (IQ) and blood pressure, and then uncovered common SNPs for these three traits. We employed SNPedia, RefSNP Report, GWAS Catalog, Gene Cards (Data Bases), PubMed and Google Scholar search engines to find relevant material on SNPs associated with three quantitative traits. As a result, we detected three common SNPs for all three quantitative traits in global populations: SNP rs6265 of the BDNF gene on chromosome 11p14.1, SNP rs131070325 of the SL39A8 gene on chromosome 4p24 and SNP rs4680 of the COMT gene on chromosome 22q11.21.

Conclusion

In our review, we focused on the prevalent SNPs and gene expression activities that influence these three quantitative traits. These SNPs have been used to detect and map complex, common illnesses in communities for homogeneity testing and pharmacogenetic studies. High blood pressure, diabetes and heart disease, as well as BMI, schizophrenia and IQ, can all be predicted using common SNPs. Finally, the results of our work can be used to find common SNPs and genes that regulate these three quantitative features across the genome.

Oscillatory connectivity as a mechanism of auditory sensory gating and its disruption in schizophrenia

Although innumerable studies using an auditory sensory gating paradigm have confirmed that individuals with schizophrenia (SZ) show less reduction in brain response to the second in a pair of clicks, this large literature has not yielded consensus on the circuit(s) responsible for gating nor for the gating difference in SZ. Clinically stable adult inpatients (N = 157) and matched community participants (N = 90) participated in a standard auditory sensory gating protocol. Responses to paired clicks were quantified as peak-to-peak amplitude from a response at approximately 50 ms to a response at approximately 100 ms in MEG-derived source waveforms. For bilateral sources in each of four regions near Heschl's gyrus, the gating ratio was computed as the response to the second stimulus divided by the response to the first stimulus. Spectrally resolved Granger causality quantified effective connectivity among regions manifested in alpha-band oscillatory coupling before and during stimulation. Poorer sensory gating localized to A1 in SZ than in controls confirmed previous results, here found in adjacent brain regions as well. Spontaneous, stimulus-independent effective connectivity within the hemisphere from angular gyrus to portions of the superior temporal gyrus was lower in SZ and correlated with gating ratio. Significant involvement of frontal and subcortical brain regions previously proposed as contributing to the auditory gating abnormality was not found. Findings point to endogenous connectivity evident in a sequence of activity from angular gyrus to portions of superior temporal gyrus as a mechanism contributing to normal and abnormal gating in SZ and potentially to sensory and cognitive symptoms.

Genetic underpinnings of schizophrenia-related electroencephalographical intermediate phenotypes: A systematic review and meta-analysis

Although substantial research into genetics of psychotic disorders has been conducted, a large proportion of their genetic architecture has remained unresolved. Electroencephalographical intermediate phenotypes (EIP) have the potential to constitute a valuable tool when studying genetic risk loci for schizophrenia, in particular P3b amplitude, P50 suppression, mismatch negativity (MMN) and resting state power spectra of the electroencephalogram (EEG). Here, we systematically reviewed studies investigating the association of single nucleotide polymorphisms (SNPs) with these EIPs and meta-analysed them when appropriate. We retrieved 45 studies (N = 34,971 study participants). Four SNPs investigated in more than one study were genome-wide significant for an association with schizophrenia and three were genome-wide suggestive, based on a lookup in the influential 2014 GWAS (Ripke et al., 2014). However, in our meta-analyses, rs1625579 failed to reach a statistically significant association with p3b amplitude decrease and rs4680 risk allele carrier status was not associated with p3b amplitude decrease or with impaired p50 suppression. In conclusion, evidence for SNP associations with EIPs remains limited to individual studies. Careful selection of EIPs and SNPs, combined with consistent reporting of effect sizes, directions of effect and p-values would aid future meta-analyses.

Genetic Determinants of Gating Functions: Do We Get Closer to Understanding Schizophrenia Etiopathogenesis?

Deficits in the gating of sensory stimuli, i.e., the ability to suppress the processing of irrelevant sensory input, are considered to play an important role in the pathogenesis of several neuropsychiatric disorders, in particular schizophrenia. Gating is disrupted both in schizophrenia patients and their unaffected relatives, suggesting that gating deficit may represent a biomarker associated with a genetic liability to the disorder. To assess the strength of the evidence for the etiopathogenetic links between genetic variation, gating efficiency, and schizophrenia, we carried out a systematic review of human genetic association studies of sensory gating (suppression of the P50 component of the auditory event-related brain potential) and sensorimotor gating (prepulse inhibition of the acoustic startle response). Sixty-three full-text articles met the eligibility criteria for inclusion in the review. In total, 117 genetic variants were reported to be associated with gating functions: 33 variants for sensory gating, 80 variants for sensorimotor gating, and four variants for both sensory and sensorimotor gating. However, only five of these associations (four for prepulse inhibition-CHRNA3 rs1317286, COMT rs4680, HTR2A rs6311, and TCF4 rs9960767, and one for P50 suppression-CHRNA7 rs67158670) were consistently replicated in independent samples. Although these variants and genes were all implicated in schizophrenia in research studies, only two polymorphisms (HTR2A rs6311 and TCF4 rs9960767) were also reported to be associated with schizophrenia at a meta-analytic or genome-wide level of evidence. Thus, although gating is widely considered as an important endophenotype of schizophrenia, these findings demonstrate that evidence for a common genetic etiology of impaired gating functions and schizophrenia is yet unsatisfactory, warranting further studies in this field.

Meta-analysis of auditory P50 sensory gating in schizophrenia and bipolar disorder

The ability of the brain to reduce the amount of trivial or redundant sensory inputs is called gating function. Dysfunction of sensory gating may lead to cognitive fragmentation and poor real-world functioning. The auditory dual-click paradigm is a pertinent neurophysiological measure of sensory gating function. This meta-analysis aimed to examine the subcomponents of abnormal P50 waveforms in bipolar disorder and schizophrenia to assess P50 sensory gating deficits and examine effects of diagnoses, illness states (first-episode psychosis vs. schizophrenia, remission vs. episodes in bipolar disorder), and treatment status (medication-free vs. medicated). Literature search of PubMed between Jan 1st 1980 and March 31st 2019 identified 2091 records for schizophrenia, 362 for bipolar disorder. 115 studies in schizophrenia (4932 patients), 16 in bipolar disorder (975 patients) and 10 in first-degree relatives (848 subjects) met the inclusion criteria. P50 sensory gating ratio (S2/S1) and S1-S2 difference were significantly altered in schizophrenia, bipolar disorder and their first-degree relatives. First-episode psychosis did not differ from schizophrenia, however episodes altered P50 sensory gating in bipolar disorder. Medications improve P50 sensory gating alterations in schizophrenia significantly and at trend level in bipolar disorder. Future studies should examine longitudinal course of P50 sensory gating in schizophrenia and bipolar disorder.

Genetic Advance in Depressive Disorder

Major depressive disorder (MDD) and bipolar disorder (BPD) are both chronic, severe mood disorder with high misdiagnosis rate, leading to substantial health and economic burdens to patients around the world. There is a high misdiagnosis rate of bipolar depression (BD) just based on symptomology in depressed patients whose previous manic or mixed episodes have not been well recognized. Therefore, it is important for psychiatrists to identify these two major psychiatric disorders. Recently, with the accumulation of clinical sample sizes and the advances of methodology and technology, certain progress in the genetics of major depression and bipolar disorder has been made. This article reviews the candidate genes for MDD and BD, genetic variation loci, chromosome structural variation, new technologies, and new methods.

Prepulse inhibition in euthymic bipolar disorder patients in comparison with control subjects

OBJECTIVE

Deficient prepulse inhibition (PPI) of the startle response, indicating sensorimotor gating deficits, has been reported in schizophrenia and other neuropsychiatric disorders. This study aimed to assess sensorimotor gating deficits in patients with euthymic bipolar. Furthermore, we analysed the relationships between PPI and clinical and cognitive measures.

METHOD

Prepulse inhibition was measured in 64 patients with euthymic bipolar and in 64 control subjects matched for age, gender, education level and smoking status. Clinical characteristics and level of functioning were assessed in all participants using Hamilton Depression Rating Scale (HDRS), Young Mania Rating Scale (YMRS) and Functioning Assessment Short Test (FAST). Cognition was evaluated using the Measurement and Treatment Research to Improve Cognition in Schizophrenia Consensus Cognitive Battery (MCCB) and the Stroop test as an additional measure of executive function.

RESULTS

Compared with controls, patients with bipolar disorder exhibited PPI deficits at 60- and 120-millisecond prepulse-pulse intervals. Among patients with bipolar disorder, PPI was correlated with the social cognition domain of the MCCB. PPI was not significantly correlated with other clinical, functional and neurocognitive variables in either group.

CONCLUSIONS

Our data suggest that PPI deficit is a neurobiological marker in euthymic bipolar disorder, which is associated with social cognition but not with other clinical, functional or cognitive measures.

Association of catechol-O-methyltransferase Val(108/158) Met genetic polymorphism with schizophrenia, P50 sensory gating, and negative symptoms in a Chinese population

Catechol-O-methyltransferase (COMT), an enzyme involved in the degradation and inactivation of the neurotransmitter dopamine, is associated with the sensory gating phenomenon, protecting the cerebral cortex from information overload. The COMT Val(108/158)Met polymorphism is essential for prefrontal cortex processing capacity and efficiency. The current study was designed to investigate the role of COMT Val(108/158)Met polymorphism in development, sensory gating deficit, and symptoms of schizophrenia in Han Chinese population. P50 gating was determined in 139 schizophrenic patients and 165 healthy controls. Positive and Negative Syndrome Scale (PANSS) was used to assess the clinical symptomatology in 370 schizophrenic subjects. COMT Val(108/158)Met polymorphism was genotyped by PCR-restriction fragment length polymorphism (PCR-RFLP). No significant differences in COMT allele and genotype distributions were observed between schizophrenic patients and control groups. Although P50 deficits were present in patients, there was no evidence for an association between COMT Val(108/158)Met polymorphism and the P50 biomarker. Moreover, PANSS negative subscore was significantly higher in Val allele carriers than in Met/Met individuals. The present findings suggest that COMT Val(108/158)Met polymorphism may not contribute to the risk of schizophrenia and to the P50 deficits, but may contribute to the negative symptoms of schizophrenia among Han Chinese.

A potential interaction between COMT and MTHFR genetic variants in Han Chinese patients with bipolar II disorder

Bipolar II disorder (BP-II), characterized by recurrent dysregulation of mood, is a serious and chronic psychiatric illness. However, BP-II is commonly under-recognized, even in psychiatric settings. Because dopaminergic disturbance is thought to be involved in the development of bipolar disorder (BPD), it seems essential to investigate dopamine-related genes like the catechol-O-methyltransferase (COMT) gene, which are involved in dopamine metabolism, and the methylenetetrahydrofolate reductase (MTHFR) gene, which may affect COMT methylation and COMT function. The current study examined the association and interaction of the COMT Val158Met and MTHFR C677T variants with BP-II. Nine hundred seventy-eight participants were recruited: 531 with BP-II and 447 healthy controls. The genotypes of the COMT and MTHFR polymorphisms were determined using a polymerase chain reaction-restriction fragment length polymorphism analysis. Logistic regression analysis showed a significant interaction effect of the COMT Val158Met Val/Val genotype and the MTHFR C677T C/T + T/T genotype (P = 0.039) for the protective effect on the odds of developing BP-II. Our findings support preliminary evidence that the COMT and MTHFR genes interact in BP-II, and they imply the connection of both dopaminergic pathways and methylation pathways in the pathogenesis of BP-II.

P50 sensory gating is a trait marker of the bipolar spectrum

Sensory gating deficit, assessed by a paired auditory stimulus paradigm (P50), has been reported as a stable marker of schizophrenia. The aim of this study was to explore if this neurophysiological disturbance also fulfilled stability criteria in the bipolar disorder (BD) spectrum bipolar, as state independence is one of the main points to be considered as a potential endophenotype of the illness. The P50 evoked potential was studied in 95 healthy controls and 126 bipolar euthymic patients. Euthymia was established according to Van Gorp's criteria. Bipolar I and II subtypes were analyzed separately. The influence of a lifetime history of psychoses was also evaluated in the clinical sample. P50 gating was deficitary in all the subsamples of patients relative to healthy comparison subjects. Bipolar I patients with and without a history of psychosis showed higher P50 ratios than the other subgroups of patients, although these differences were not significant. P50 alterations were mainly due to a deficit in the inhibition of the second wave (test wave or S2) amplitude.

CONCLUSIONS

The findings suggest that this inhibitory deficit can be considered characteristic of the illness and that the intensity of the gating abnormality varies according to the severity of BD.

[Schizophrenia and/or bipolar disorder: the neurocognitive endophenotypes]

Although Kraepelinian dichotomous conceptualization of psychosis was historically beneficial, modern studies do not support the existence of a sub-typing of psychotic illnesses into schizophrenic and affective psychoses. Years of intensive investigation on the genetic bases of schizophrenia and bipolar disorder suggest that these disorders, rather than being wholly distinct disorders, share common genetic risks. However, one of the most serious difficulties for genetic research in these illnesses is their enormous phenotypic heterogeneity. A response to this problem is the use of neurocognitive functions as endophenotypes or intermediate phenotypes. A review of the literature suggests that in both schizophrenia and bipolar disorder, neurocognitive functions are influenced by genetic factors and that there exists neuropsychological deficits in the nonaffected relatives of probands. However, it is unclear whether or not patterns of performance on neurocognitive tasks across probands as well as unaffected family members offer potential for identifying shared and illness-specific neurocognitive phenotypes for schizophrenia and bipolar disorder. Overlapping and unique neurocognitive endophenotypic signatures of the two psychoses are comprehensively described.