Does COMT val158met polymorphism influence P50 sensory gating, eye tracking or saccadic inhibition dysfunctions in schizophrenia?

Catechol-O-methyltransferase (COMT) Val158Met Polymorphism and Prepulse Inhibition of the Change-related Cerebral Response

Change-related potentials elicited by an abrupt sound feature's change are attenuated by a leading weak sound (prepulse inhibition: PPI). We investigated whether the PPI index is associated with the catechol-methyltransferase (COMT) Val158Met polymorphism (rs4680), which is involved in the metabolism of dopamine in the prefrontal cortex. Healthy subjects with normal hearing were recruited (n = 70). A train of 100-Hz clicks 650 ms in duration was used. The test stimulus was an abrupt increase in sound intensity (+10 dB) from the baseline (70 dB) provided at 400 ms after the sound onset. Three consecutive clicks at 30, 40, and 50 ms before the change's onset were greater (+3 or +5 dB) from the baseline as a prepulse. The targeting auditory evoked potential component was Change-N1 peaking approx. 130 ms after the change onset. We calculated the inhibition level as the% inhibition of the Change-N1 amplitude by a prepulse. The %PPI in the Met-carriers was significantly greater than that in the Val/Val-individuals. Our results suggest that dopamine might play a role in the PPI of the change-related response. We propose that this index has the potential to identify an intermediate phenotype in psychiatric disorders such as schizophrenia.

Comparative Analysis of Dopaminergic and Cholinergic Mechanisms of Sensory and Sensorimotor Gating in Healthy Individuals and in Patients With Schizophrenia

Sensory and sensorimotor gating provide the early processing of information under conditions of rapid presentation of multiple stimuli. Gating deficiency is observed in various psychopathologies, in particular, in schizophrenia. However, there is also a significant proportion of people in the general population with low filtration rates who do not show any noticeable cognitive decline. The review article presents a comparative analysis of existing data on the peculiarities of cholinergic and dopaminergic mechanisms associated with lowering gating in healthy individuals and in patients with schizophrenia. The differences in gating mechanisms in cohorts of healthy individuals and those with schizophrenia are discussed.

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.

Sensory Inhibition Is Related to Variable Speech Perception in Noise in Adults With Normal Hearing

Purpose Speech perception in noise (SPiN) varies widely in individuals with normal hearing, which may be attributed to factors that are not reflected in the audiogram, such as inhibition. However, inhibition is involved at both sensory and cognitive stages of auditory perception, and while inhibition at the cognitive level has been shown to be a significant factor in SPiN processes, it is unknown whether sensory inhibition may also contribute to SPiN variability. Therefore, the goal of this study was to evaluate sensory inhibition in adults with normal hearing and mild SPiN impairment. Method Cortical auditory evoked potentials (CAEPs) were recorded in 49 adults via high-density electroencephalography using an auditory gating paradigm. Participants were categorized according to a median signal-to-noise ratio (SNR) loss of 1.5 dB: typical SNR loss ≤ 1.5 dB (n = 32), mild SNR loss > 1.5 dB (n = 17). CAEP gating responses were compared and correlated with SNR loss and extended high-frequency thresholds. Current density reconstructions were performed to qualitatively observe underlying cortical inhibitory networks in each group. Results In comparison to adults with typical SPiN ability, adults with mild SPiN impairment showed an absence of the gating response. A CAEP gating component (P2) reflected decreased sensory inhibition and correlated with increased SNR loss. Extended high-frequency thresholds were also found to correlate with SNR loss, but not gating function. An atypical cortical inhibitory network was observed in the mild SNR loss group, with reduced frontal and absent prefrontal activation. Conclusion Sensory inhibition appears to be atypical and related to SPiN deficits in adults with mild impairment. In addition, cortical inhibitory networks appear to be incomplete, with a possible compensatory parietal network. Further research is needed to delineate between types or levels of central inhibitory mechanisms and their contribution to SPiN processes.

COMT and GAD1 gene polymorphisms are associated with impaired antisaccade task performance in schizophrenic patients

Genetic influences modulating executive functions engaging prefrontal cortical brain systems were investigated in 141 male subjects. The effects of variations in two genes implicated in dopamine and GABA activities in the prefrontal cortex: rs4680 (Val158/Met polymorphism of the catechol-o-methyltransferase gene-COMT) and rs3749034 (C/T) substitution in the promoter region of the glutamic acid decarboxylase gene (GAD1) were studied on antisaccade (AS) performance in healthy subjects and schizophrenic patients. Genotyping revealed a trend towards a reduced proportion of COMT Val/Met heterozygotes and a significantly increased frequency of the GAD1 rs3749034 C allele in schizophrenic patients relative to controls. Patients had elevated error rates, increased AS latencies and increased latency variability (coefficient of variation) compared to controls. The influence of polymorphisms was observed only in patients but not in controls. A substantial effect of the COMT genotype was noted on the coefficient of variation in latency, and this measure was higher in Val homozygotes compared to Met allele carriers (p < 0.05) in the patient group. The outcome from rs3749034 was also disclosed on the error rate (higher in T carriers relative to C homozygotes, p < 0.01) and latency (increased in C homozygotes relative to T carriers, p < 0.01). Binary logistic regression showed that inclusion of the genotype factor (i.e., selective estimation of antisaccade measures in CC carriers) considerably increased the validity of the diagnostic model based on the AS measures. These findings may well be derived from specific genetic associations with prefrontal cortex functioning in schizophrenia.

The Role of Dopamine in Anticipatory Pursuit Eye Movements: Insights from Genetic Polymorphisms in Healthy Adults

There is a long history of eye movement research in patients with psychiatric diseases for which dysfunctions of neurotransmission are considered to be the major pathologic mechanism. However, neuromodulation of oculomotor control is still hardly understood. We aimed to investigate in particular the impact of dopamine on smooth pursuit eye movements. Systematic variability in dopaminergic transmission due to genetic polymorphisms in healthy subjects offers a noninvasive opportunity to determine functional associations. We measured smooth pursuit in 110 healthy subjects genotyped for two well-documented polymorphisms, the COMT Val¹⁵⁸Met polymorphism and the SLC6A3 3′-UTR-VNTR polymorphism. Pursuit paradigms were chosen to particularly assess the ability of the pursuit system to initiate tracking when target motion onset is blanked, reflecting the impact of extraretinal signals. In contrast, when following a fully visible target sensory, retinal signals are available. Our results highlight the crucial functional role of dopamine for anticipatory, but not for sensory-driven, pursuit processes. We found the COMT Val¹⁵⁸Met polymorphism specifically associated with anticipatory pursuit parameters, emphasizing the dominant impact of prefrontal dopamine activity on complex oculomotor control. In contrast, modulation of striatal dopamine activity by the SLC6A3 3′-UTR-VNTR polymorphism had no significant functional effect. Though often neglected so far, individual differences in healthy subjects provide a promising approach to uncovering functional mechanisms and can be used as a bridge to understanding deficits in patients.