Association of EEG coherence and an exonic GABA(B)R1 gene polymorphism

Variants in GABBR1 Gene Are Associated with Methamphetamine Dependence and Two Years' Relapse after Drug Rehabilitation

Methamphetamine (MA) use disorder is a growing global health challenge marked by a steady increase worldwide. GABAergic system plays an important role in the mechanism of drug dependence, however few studies about the association between methamphetamine use disorder and genes in GABAergic system. Concerning GABBR1 gene which encoding the GABAB receptor subunit 1 is an important regulator in the GABAergic system. The aim of the study is to explore whether GABBR1 gene play a role in methamphetamine dependence and relapse after rehabilitation. Three single nucleotide polymorphisms (SNPs, rs2076483, rs29221, rs715044) of the GABBR1 gene were genotyped in 791 participants with MA use disorder and 448 healthy controls. The distribution of genotypes and alleles of the three SNPs between the two groups and their subgroups (dependence and abuse) was been analyzed. The multivariate logistic model was used to identify factors associate with relapse of MA use disorder during the following 2 years after drug rehabilitation. It was found that the C allele frequency of rs715044 of the GABBR1 gene was associated with MA use disorder and MA dependence. The CGA (rs2076483- rs29221- rs715044) was negatively associated with MA use disorder. The drug use years and rs29221 GG genotype were associated with relapse during the following 2 years after drug rehabilitation. GABBR1 gene may be associated with the susceptibility for MA use disorder and relapse and it indicates that the GABAergic system may play a role in the MA use disorder. Graphical Abstract GABBR1 gene may be associated with the susceptibility for MA use disorder and relapse and it indicates that the GABAergic system may play a role in the MA use disorder.

Neural connectivity in Internet gaming disorder and alcohol use disorder: A resting-state EEG coherence study

The present study compared neural connectivity and the level of phasic synchronization between neural populations in patients with Internet gaming disorder (IGD), patients with alcohol use disorder (AUD), and healthy controls (HCs) using resting-state electroencephalography (EEG) coherence analyses. For this study, 92 adult males were categorized into three groups: IGD (n = 30), AUD (n = 30), and HC (n = 32). The IGD group exhibited increased intrahemispheric gamma (30-40 Hz) coherence compared to the AUD and HC groups regardless of psychological features (e.g., depression, anxiety, and impulsivity) and right fronto-central gamma coherence positively predicted the scores of the Internet addiction test in all groups. In contrast, the AUD group showed marginal tendency of increased intrahemispheric theta (4-8 Hz) coherence relative to the HC group and this was dependent on the psychological features. The present findings indicate that patients with IGD and AUD exhibit different neurophysiological patterns of brain connectivity and that an increase in the fast phasic synchrony of gamma coherence might be a core neurophysiological feature of IGD.

[Molecular-genetic and electroencephalographic markers of neurocognitive processes in depressive disorders]

Perspectives of molecular-genetic approaches to the establishment of mechanisms of development and causes of heterogeneity of neurocognitive impairment are discussed. The current results indicate that candidate genes for depression can contribute to the variance of memory and regulatory functions in patients. At the same time, these genes are closely related to affective information processing and .cortisol level. By that fact, it can't be excluded that affective processes moderate the association between cognition and genes. EEG parameters could be useful phenotypes in the search for and understanding of genetic mechanisms of cognitive deficit in depression. Parameters of resting EEG and its reactive changes are known to reflect the certain cognitive processes. They are influenced by genetic factors and are sensitive indicators of mechanisms that might underlie cognitive impairment in depressive patients. Accumulating data on molecular-genetic correlates of normal electric brain activity may be a source of choosing new candidate genes for cognitive impairment in depression.

Genetics of alcohol dependence: a review of clinical studies

BACKGROUND/AIMS

Alcohol dependence is a common severe psychiatric disorder with a multifactorial etiology. Since the completion of the human genome project and with the increased availability of high-throughput genotyping, multiple genetic risk factors for substance-related disorders, including alcohol dependence, have been identified, but not all results could be replicated.

METHODS

We systematically review the clinical literature on genetic risk factors for alcohol dependence and alcohol-related phenotypes, including candidate gene-based studies, linkage studies and genome-wide association studies (GWAS).

RESULTS

Irrespectively of the methodology employed, the most robust findings regarding genetic risk factors for alcohol dependence concern genetic variations that affect alcohol metabolism. GWAS confirm the importance of the alcohol dehydrogenase gene cluster on chromosome 4 in the genetic risk for alcohol dependence with multiple variants that exert a small, but cumulative influence. A single variant with strong influence on individual risk is the aldehyde dehydrogenase 2 ALDHD2*2 variant common in Asian populations. Other robust associations have been found with previously uncharacterized genes like KIAA0040, and such observations can lead to the identification of thus far unknown signaling pathways. Converging evidence also points to a role of glutamatergic, dopaminergic and serotonergic neurotransmitter signaling in the risk for alcohol dependence, but effects are small, and gene-environment interactions further increase the complexity.

CONCLUSION

With few exceptions like ALDH2*2, the contribution of individual genetic variants to the risk for alcohol-related disorders is small. However, the concentration of risk variants within neurotransmitter signaling pathways may help to deepen our understanding of the underlying pathophysiology and thereby contribute to develop novel therapeutic strategies.

Altered resting-state EEG source functional connectivity in schizophrenia: the effect of illness duration

Despite the increasing body of evidence supporting the hypothesis of schizophrenia as a disconnection syndrome, studies of resting-state EEG Source Functional Connectivity (EEG-SFC) in people affected by schizophrenia are sparse. The aim of the present study was to investigate resting-state EEG-SFC in 77 stable, medicated patients with schizophrenia (SCZ) compared to 78 healthy volunteers (HV). In order to study the effect of illness duration, SCZ were divided in those with a short duration of disease (SDD; n = 25) and those with a long duration of disease (LDD; n = 52). Resting-state EEG recordings in eyes closed condition were analyzed and lagged phase synchronization (LPS) indices were calculated for each ROI pair in the source-space EEG data. In delta and theta bands, SCZ had greater EEG-SFC than HV; a higher theta band connectivity in frontal regions was observed in LDD compared with SDD. In the alpha band, SCZ showed lower frontal EEG-SFC compared with HV whereas no differences were found between LDD and SDD. In the beta1 band, SCZ had greater EEG-SFC compared with HVs and in the beta2 band, LDD presented lower frontal and parieto-temporal EEG-SFC compared with HV. In the gamma band, SDD had greater connectivity values compared with LDD and HV. This study suggests that resting state brain network connectivity is abnormally organized in schizophrenia, with different patterns for the different EEG frequency components and that EEG can be a powerful tool to further elucidate the complexity of such disordered connectivity.

GABA Receptors Genes Polymorphisms and Alcohol Dependence: No Evidence of an Association in an Italian Male Population

Objective

The genes encoding for gamma-aminobutyric acid (GABA) A and B receptors may be considered as candidates for alcoholism; genetic alterations at this level may produce structural and functional diversity and thus play a role in the response to alcohol addiction treatment. To investigate these aspects further, we conducted a preliminary genetic association study on a population of Italian male alcohol addicts, focusing on GABA A and B receptors.

Methods

A total of 186 alcohol-dependent subjects (in the first phase 139, then 47 more samples) and 182 controls were genotyped for 25 single nucleotide polymorphisms (SNPs) of genes encoding the alpha-1 subunit of GABA A receptor (GABRA1) and subunits 1 and 2 of GABA B receptor (GABBR1 and GABBR2). The chi-squared test for allele and genotype distributions and Hardy-Weinberg equilibrium analysis of both subjects and controls were performed. Bonferroni's correction for multiple comparisons was applied.

Results

Preliminary results comparing 139 alcohol-dependent subjects and 182 controls showed differences in genotype distribution in the former for SNP rs29253, located in the intron region of the GABBR1 gene. In order to clarify the meaning of this association, 47 more samples from alcohol-dependent subjects were tested for this SNP only: the previously found association was not confirmed.

Conclusion

The lack of significant differences between the two groups does not provide evidence that GABRA 1 and GABBR1 and 2 genes are candidates for alcoholism in this population. Further studies with larger samples are needed, together with investigation of other components of the GABA pathway.

Genetic psychophysiology: advances, problems, and future directions

This paper presents an overview of historical advances and the current state of genetic psychophysiology, a rapidly developing interdisciplinary research linking genetics, brain, and human behavior, discusses methodological problems, and outlines future directions of research. The main goals of genetic psychophysiology are to elucidate the neural pathways and mechanisms mediating genetic influences on cognition and emotion, identify intermediate brain-based phenotypes for psychopathology, and provide a functional characterization of genes being discovered by large association studies of behavioral phenotypes. Since the initiation of this neurogenetic approach to human individual differences in the 1970s, numerous twin and family studies have provided strong evidence for heritability of diverse aspects of brain function including resting-state brain oscillations, functional connectivity, and event-related neural activity in a variety of cognitive and emotion processing tasks, as well as peripheral psychophysiological responses. These data indicate large differences in the presence and strength of genetic influences across measures and domains, permitting the selection of heritable characteristics for gene finding studies. More recently, candidate gene association studies began to implicate specific genetic variants in different aspects of neurocognition. However, great caution is needed in pursuing this line of research due to its demonstrated proneness to generate false-positive findings. Recent developments in methods for physiological signal analysis, hemodynamic imaging, and genomic technologies offer new exciting opportunities for the investigation of the interplay between genetic and environmental factors in the development of individual differences in behavior, both normal and abnormal.

Understanding alcohol use disorders with neuroelectrophysiology

Neurocognitive deficits associated with impairments in various brain regions and neural circuitries, particularly involving frontal lobes, have been associated with chronic alcoholism, as well as with a predisposition to develop alcohol use and related disorders (AUDs). AUD is a multifactorial disorder caused by complex interactions between behavioral, genetic, and environmental liabilities. Neuroelectrophysiologic techniques are instrumental in understanding brain and behavior relationships and have also proved very useful in evaluating the genetic diathesis of alcoholism. This chapter describes findings from neuroelectrophysiologic measures (electroencephalogram, event-related potentials, and event-related oscillations) related to acute and chronic effects of alcohol on the brain and those that reflect underlying deficits related to a predisposition to develop AUDs and related disorders. The utility of these measures as effective endophenotypes to identify and understand genes associated with brain electrophysiology, cognitive networks, and AUDs has also been discussed.

A thalamic reticular networking model of consciousness

[BACKGROUND]: It is reasonable to consider the thalamus a primary candidate for the location of consciousness, given that the thalamus has been referred to as the gateway of nearly all sensory inputs to the corresponding cortical areas. Interestingly, in an early stage of brain development, communicative innervations between the dorsal thalamus and telencephalon must pass through the ventral thalamus, the major derivative of which is the thalamic reticular nucleus (TRN). The TRN occupies a striking control position in the brain, sending inhibitory axons back to the thalamus, roughly to the same region where they receive afferents. [HYPOTHESES]: The present study hypothesizes that the TRN plays a pivotal role in dynamic attention by controlling thalamocortical synchronization. The TRN is thus viewed as a functional networking filter to regulate conscious perception, which is possibly embedded in thalamocortical networks. Based on the anatomical structures and connections, modality-specific sectors of the TRN and the thalamus appear to be responsible for modality-specific perceptual representation. Furthermore, the coarsely overlapped topographic maps of the TRN appear to be associated with cross-modal or unitary conscious awareness. Throughout the latticework structure of the TRN, conscious perception could be accomplished and elaborated through accumulating intercommunicative processing across the first-order input signal and the higher-order signals from its functionally associated cortices. As the higher-order relay signals run cumulatively through the relevant thalamocortical loops, conscious awareness becomes more refined and sophisticated. [CONCLUSIONS]: I propose that the thalamocortical integrative communication across first- and higher-order information circuits and repeated feedback looping may account for our conscious awareness. This TRN-modulation hypothesis for conscious awareness provides a comprehensive rationale regarding previously reported psychological phenomena and neurological symptoms such as blindsight, neglect, the priming effect, the threshold/duration problem, and TRN-impairment resembling coma. This hypothesis can be tested by neurosurgical investigations of thalamocortical loops via the TRN, while simultaneously evaluating the degree to which conscious perception depends on the severity of impairment in a TRN-modulated network.

EEG alpha phenotypes: linkage analyses and relation to alcohol dependence in an American Indian community study

BACKGROUND

Evidence for a high degree of heritability of EEG alpha phenotypes has been demonstrated in twin and family studies in a number of populations. However, information on linkage of this phenotype to specific chromosome locations is still limited. This study's aims were to map loci linked to EEG alpha phenotypes and to determine if there was overlap with loci previously mapped for alcohol dependence in an American Indian community at high risk for substance dependence.

METHODS

Each participant gave a blood sample and completed a structured diagnostic interview using the Semi Structured Assessment for the Genetics of Alcoholism. Bipolar EEGs were collected and spectral power determined in the alpha (7.5-12.0 Hz) frequency band for two composite scalp locations previously identified by principal components analyses (bilateral fronto-central and bilateral centro-parietal-occipital). Genotypes were determined for a panel of 791 micro-satellite polymorphisms in 410 members of multiplex families using SOLAR.

RESULTS

Sixty percent of this study population had a lifetime diagnosis of alcohol dependence. Analyses of multipoint variance component LOD scores, for the EEG alpha power phenotype, revealed two loci that had a LOD score of 3.0 or above for the fronto-central scalp region on chromosomes 1 and 6. Additionally, 4 locations were identified with LOD scores above 2.0 on chromosomes 4, 11, 14, 16 for the fronto-central location and one on chromosome 2 for the centro-parietal-occipital location.

CONCLUSION

These results corroborate the importance of regions on chromosome 4 and 6 highlighted in prior segregation studies in this and other populations for alcohol dependence-related phenotypes, as well as other areas that overlap with other substance dependence phenotypes identified in previous linkage studies in other populations. These studies additionally support the construct that EEG alpha recorded from fronto-central scalp areas may represent an important endophenotype associated with alcohol and other substance dependence.

EEG spectral phenotypes: heritability and association with marijuana and alcohol dependence in an American Indian community study

Native Americans have some of the highest rates of marijuana and alcohol use and abuse, yet neurobiological measures associated with dependence on these substances in this population remain unknown. The present investigation evaluated the heritability of spectral characteristics of the electroencephalogram (EEG) and their correlation with marijuana and alcohol dependence in an American Indian community. Participants (n=626) were evaluated for marijuana (MJ) and alcohol (ALC) dependence, as well as other psychiatric disorders. EEGs were collected from six cortical sites and spectral power determined in five frequency bands (delta 1.0-4.0 Hz, theta 4.0-7.5 Hz, alpha 7.5-12.0 Hz, low beta 12.0-20.0 Hz and high beta/gamma 20-50 Hz). The estimated heritability (h(2)) of the EEG phenotypes was calculated using SOLAR, and ranged from 0.16 to 0.67. Stepwise linear regression was used to detect correlations between MJ and ALC dependence and the spectral characteristics of the EEG using a model that took into account: age, gender, Native American Heritage (NAH) and a lifetime diagnosis of antisocial personality and/or conduct disorder (ASPD/CD). Increases in spectral power in the delta frequency range, were significantly correlated with gender (p<0.001) and marijuana dependence (p<0.003). Gender, age, NAH and ASPD/CD were all significantly (p<0.001) correlated with theta, alpha and beta band power, whereas alcohol dependence (p<0.01), gender (p<0.001), and ASPD/CD (p<0.001) were all correlated with high beta/gamma band power. These data suggest that the traits of EEG delta and high beta/gamma activity are correlated with MJ dependence and alcohol dependence, respectively, in this community sample of Native Americans.

Uncovering genes for cognitive (dys)function and predisposition for alcoholism spectrum disorders: a review of human brain oscillations as effective endophenotypes

Brain oscillations provide a rich source of potentially useful endophenotypes (intermediate phenotypes) for psychiatric genetics, as they represent important correlates of human information processing and are associated with fundamental processes from perception to cognition. These oscillations are highly heritable, are modulated by genes controlling neurotransmitters in the brain, and provide links to associative and integrative brain functions. These endophenotypes represent traits that are less complex and more proximal to gene function than either diagnostic labels or traditional cognitive measures, providing a powerful strategy in searching for genes in psychiatric disorders. These intermediate phenotypes identify both affected and unaffected members of an affected family, including offspring at risk, providing a more direct connection with underlying biological vulnerability. Our group has utilized heritable neurophysiological features (i.e., brain oscillations) as endophenotypes, making it possible to identify susceptibility genes that may be difficult to detect with diagnosis alone. We have discussed our findings of significant linkage and association between brain oscillations and genes in GABAergic, cholinergic and glutamatergic systems (GABRA2, CHRM2, and GRM8). We have also shown that some oscillatory indices from both resting and active cognitive states have revealed a common subset of genetic foci that are shared with the diagnosis of alcoholism and related disorders. Implications of our findings have been discussed in the context of physiological and pharmacological studies on receptor function. These findings underscore the utility of quantitative neurophysiological endophenotypes in the study of the genetics of brain function and the genetic diathesis underlying complex psychiatric disorders.

QTLs identified for P3 amplitude in a non-clinical sample: importance of neurodevelopmental and neurotransmitter genes

BACKGROUND

The P3(00) event-related potential is an index of processing capacity (P3 amplitude) and stimulus evaluation (P3 latency) as well as a phenotypic marker of various forms of psychopathology where P3 abnormalities have been reported.

METHODS

A genome-wide linkage scan of 400-761 autosomal markers, at an average spacing of 5-10 centimorgans (cM), was completed in 647 twins/siblings (306 families mostly comprising dizygotic twins), mean age 16.3, range 15.4-20.1 years, for whom P3 amplitude and latency data were available.

RESULTS

Significant linkage for P3 amplitude was observed on chromosome 7q for the central recording site (logarithm-of-odds [LOD] = 3.88, p = .00002) and in the same region for both frontal (LOD = 2.19, p = .0015) and parietal (LOD = 1.67, p = .0053) sites, with multivariate analysis also identifying linkage in this region (LOD = 2.14, p = .0017). Suggestive linkage was also identified on 6p (LOD(max) = 2.49) and 12q (LOD(max) = 2.24), with other promising regions identified on 9q (LOD(max) = 2.14) and 10p (LOD(max) = 2.18). Less striking were the results for P3 latency; LOD > 1.5 were found on chromosomes 1q, 9q, 10q, 12q, and 19p.

CONCLUSIONS

This is a first step in the identification of genes for normal variation in the P3. Loci identified here for P3 amplitude suggest the possible importance of neurodevelopmental genes in addition to those influencing neurotransmitters, fitting with the evidence that P3 amplitude is sensitive to diverse types of brain abnormalities.

EEG biofeedback as a treatment for substance use disorders: review, rating of efficacy, and recommendations for further research

Electroencephalographic (EEG) biofeedback has been employed in substance use disorder (SUD) over the last three decades. The SUD is a complex series of disorders with frequent comorbidities and EEG abnormalities of several types. EEG biofeedback has been employed in conjunction with other therapies and may be useful in enhancing certain outcomes of therapy. Based on published clinical studies and employing efficacy criteria adapted by the Association for Applied Psychophysiology and Biofeedback and the International Society for Neurofeedback and Research, alpha theta training-either alone for alcoholism or in combination with beta training for stimulant and mixed substance abuse and combined with residential treatment programs, is probably efficacious. Considerations of further research design taking these factors into account are discussed and descriptions of contemporary research are given.

Association of GABA(B)R1 receptor gene polymorphism with obstructive sleep apnea syndrome

OBJECTIVE

GABA(B)R (gamma-amino butyric acid B receptor)-mediated neurotransmission has been implicated in the pathophysiology of a variety of neuropsychiatric disorders. GABA(B)R1 gene variants were identified by single-strand conformation analysis. The nucleotide exchanges cause a substitution of alanine to valine in exon 1a1 (Ala20Val), a substitution of glycine to serine in exon 7 (Gly489Ser) and a silent C to G nucleotide exchange encoding the amino acid phenylalanine in exon 11 (Phe658Phe). The significance of GABA(B)R1a gene polymorphism in obstructive sleep apnea syndrome (OSAS) as well as the association of these polymorphisms with the polysomnography findings in OSAS patients are not known. In this study, we aimed to assess the significance of 3 different GABA(B)R1 gene polymorphisms (Ala20Val, Gly489Ser and Phe658Phe) in OSAS.

METHODS

Seventy-five patients (23 female and 52 male) with OSAS and 99 healthy volunteers (51 female, 48 male) were included in the study to assess Ala20Val, Gly489Ser and Phe658Phe polymorphisms of the GABA(B)R1 gene.

RESULTS

For the Ala20Val variants, there was no significant difference between the genotypes and allele frequencies of the patients and controls, nor between both genders (p > 0.05). For Phe658Phe polymorphism, there was no significant difference between genotypes and allele frequencies of the patients and controls (p > 0.05). However, the C/C genotype was overrepresented and the T/C genotype was less frequent in male than female patients (p = 0.03). The C/C genotype was overrepresented and the T/C genotype was less frequent in male patients than male controls (p = 0.01). For GABA(B)R1-Gly489Ser polymorphism, all of the patients and controls had G/G genotype. The apnea arousal index scores of the male patients with C/C genotype were significantly higher than in the patients with C/T genotype (p = 0.01). The percent total sleep time in non-REM 1 scores of the male patients with T/T genotype were significantly higher than in the patients with T/C genotype (p = 0.021). The percent total sleep time in non-REM 2 scores of the female patients with C/C genotype were significantly higher than in the patients with C/T genotype (p = 0.006).

CONCLUSION

The Ala20Val polymorphism of the GABA(B)R1 gene may be associated with OSAS, whereas Gly489Ser polymorphism does not seem to be involved in OSAS. The C/C variant of the Phe658Phe polymorphism GABA(B)R1 gene seems associated with the occurrence of OSAS and is also associated with some sleep related parameters (apnea arousal index and percent total sleep time in non-REM) recorded by polysomnography.

The polymorphism GABABR1 T1974C[rs29230] of the GABAB receptor gene is not associated with the diagnosis of alcoholism or alcohol withdrawal seizures

As the inhibitory neurotransmitter gamma aminobutyric acid (GABA) modulates ethanol consumption, alcohol withdrawal symptoms and seizure generation by interacting with the GABAB receptor, the genes encoding for the GABAB receptor can be considered as candidate genes for alcoholism and alcohol withdrawal seizures (AWS). As the polymorphism GABABR1 T1974C[rs29230] of the GABAB receptor gene had been associated with alcoholism and EEG abnormalities in prior studies, the present examination investigated if the polymorphism is associated with the diagnosis of alcoholism or AWS. After genotyping the allele and genotype frequencies of a group of alcoholics with a history of AWS (n = 69) were compared with the results of a group of alcoholics with only mild withdrawal symptoms (n = 97). Additionally a group of healthy controls (n = 101) was compared with individuals with the diagnosis of alcoholism (n = 220). As no significant differences were found between the compared groups, this study gave no further evidence for GABABR1 T1974C[rs29230] as a candidate for alcoholism or AWS.

Moderate-to-heavy alcohol intake is associated with differences in synchronization of brain activity during rest and mental rehearsal

In alcohol-dependent individuals, synchronization of brain activity is different from that in non-alcohol-dependent individuals as reflected by EEG differences at alpha and beta frequencies (8-30 Hz). These EEG differences may not only be related to long-term alcohol intake but also to genetic factors that are associated with alcohol dependence. Thus, it is not known what the pure effect of long-term alcohol intake on synchronization of brain activity is. Therefore, we investigated whether EEG synchronization differs between light (0.5-6 drinks per week), moderate (7-20 drinks per week), and heavy (21-53 drinks per week) drinkers. All participants (49 males and 47 females) were free of a personal and family history of alcohol dependence. Eyes-closed EEG was recorded at rest and during mental rehearsal of pictures. EEG synchronization was determined by computing Synchronization Likelihood for six frequency bands (0.5-4 Hz, 4-8 Hz, 8-12 Hz, 12-20 Hz, 20-30 Hz, 30-45 Hz). Both male and female heavy drinkers displayed a loss of lateralization in alpha (8-12 Hz) and slow-beta (12-20 Hz) synchronization. In addition, moderately and heavily drinking males had lower fast-beta (20-30 Hz) synchronization than lightly drinking males. It is concluded that both male and female drinkers who drink 21 alcoholic drinks per week or more have impaired synchronization of brain activity during rest and mental rehearsal at alpha and beta frequencies as compared to individuals who drink less. As individuals with a personal or family history of alcohol dependence were excluded, the confounding effects of genetic factors related to alcohol dependence on synchronization of brain activity were minimized.

Endophenotypes in the Genetic Analyses of Mental Disorders

Common mental disorders such as schizophrenia, bipolar disorder, and severe major depression are highly heritable, but differ from single-gene (Mendelian) diseases in that they are the end products of multiple causes. Although this fact may help explain their prevalence from an evolutionary perspective, the complexity of the causes of these disorders makes identification of disease-promoting genes much more difficult. The "endophenotype" approach is an alternative method for measuring phenotypic variation that may facilitate the identification of susceptibility genes for complexly inherited traits. Here we examine the endophenotype construct in context of psychiatric genetics. We first develop an evolutionary theoretical framework for common mental disorders and differentiate them from simpler, single-gene disorders. We then provide a definition and description of endophenotypes, elucidating several features that will make a proposed endophenotype useful in psychiatric genetic research and evaluating the methods for detecting and validating such endophenotypes. We conclude with a review of recent results in the schizophrenia literature that illustrate the usefulness of endophenotypes in genetic analyses of mental disorders, and discuss implications of these findings for models of disease causation and nosology. Given that in mental disorders as in behavior generally, the pathways from genotypes to phenotypes are circuitous at best, discernment of endophenotypes more proximal to the effects of genetic variation will aid attempts to link genes to disorders.

Genetics of human brain oscillations

In the last three decades, much emphasis has been placed on neural oscillations in vitro, in vivo, as well as in the human brain. These brain oscillations have been studied extensively in the resting electroencephalogram (EEG), as well as in the underlying evoked oscillations that make up the event-related potentials (ERPs). There are several approaches to elucidate the possible mechanisms of these brain oscillations. One approach is to look at the neurophysiology and neurochemistry involved in generating and modulating these oscillations. Another more recent approach is to examine the genetic underpinnings of these neural oscillations. It is proposed that the genetic underpinnings of these oscillations are likely to stem from regulatory genes which control the neurochemical processes of the brain, and therefore influence neural function. Genetic analyses of human brain oscillations may identify genetic loci underlying the functional organization of human neuroelectric activity. Brain oscillations represent important correlates of human information processing and cognition. They represent highly heritable traits that are less complex and more proximal to gene function than either diagnostic labels or traditional cognitive measures. Therefore these oscillations may be utilized as phenotypes of cognition and as valuable tools for the understanding of some complex genetic disorders. Genetic loci that have been recently identified regarding both resting and evoked brain oscillations involving the GABAergic and cholinergic neurotransmitter systems of the brain are discussed. It is concluded that the advent of genomics and proteomics and a fuller understanding of gene regulation will open new horizons on the critical electrical events so essential for human brain function.

The utility of neurophysiological markers in the study of alcoholism

OBJECTIVE

This review attempts to differentiate neuroelectric measures (electroencephalogram (EEG), event-related potentials (ERPs) and event-related oscillations (EROs)) related to acute and chronic effects of alcohol on the brain from those that reflect underlying deficits related to the predisposition to develop alcoholism and related disorders. The utility of these neuroelectric measures as endophenotypes for psychiatric genetics is evaluated.

METHODS

This article reviews the main findings of EEG and ERP abnormalities in alcoholics, offspring of alcoholics at high risk to develop alcoholism and the electrophysiological effects of alcohol on high risk compared to low-risk offspring. It highlights findings using EROs, a fast developing tool in examining brain function and cognition. It also reviews evidence of genetic findings related to these electrophysiological measures and their relationship to clinical diagnosis.

RESULTS

Many of these abnormal neuroelectric measures are under genetic control, may precede the development of alcoholism, and may be markers of a predisposition toward the development of a spectrum of disinhibitory conditions including alcoholism. Genetic loci underlying some neuroelectic measures that involve neurotransmitter systems of the brain have been identified.

CONCLUSIONS

Quantitative neuroelectric measures (EEG, ERPs, EROs) provide valuable endophenotypes in the study of genetic risk to develop alcoholism and related disorders.

SIGNIFICANCE

Genetic studies of neuroelectric endophenotypes offer a powerful strategy for identifying susceptibility genes for developing psychiatric disorders, and provide novel insights into etiological factors.

The inheritance of intermediate phenotypes for schizophrenia

PURPOSE OF REVIEW

While schizophrenia is substantially heritable, the mode of inheritance is complex, involving numerous genes of small effect and a non-trivial environmental component. The 'endophenotype' approach is an alternative method for measuring phenotypic variation that may facilitate the identification of susceptibility genes in the context of complexly inherited traits. Here we review recent studies applying this method to measures of brain structure, physiology, and function in samples of schizophrenia patients and their non-ill first-degree relatives (siblings and co-twins).

RECENT FINDINGS

The results suggest that there are multiple heritable dimensions of central nervous system pathology in schizophrenia, including disturbances in the structure and functioning of frontal lobe systems involved in working memory and executive processes, temporal lobe systems involved in episodic memory, auditory perception, and language processing, and cortical and sub-cortical systems mediating smooth pursuit eye movements and sensorimotor gating. A number of genetic loci that are suspected to play a role in predisposing to schizophrenia, including the DISC1, COMT, neuregulin, dysbindin, and alpha-7 nicotinic receptor genes, appear to affect quantitative variation on one or more of these indicators.

SUMMARY

Future work is encouraged to address whether each of these neural system dysfunctions are under the influence of a partially distinct set of genes, to elucidate the manner in which multiple genes may coalesce in determining schizophrenia-promoting dysfunction in each neurobehavioral domain, and to clarify the degree of overlap in these quantitative trait loci-endophenotype relationships with other forms of psychosis, particularly bipolar disorder.

EEG phenotype in alcoholism: increased coherence in the depressive subtype

OBJECTIVE

Electroencephalography (EEG) power and coherence changes may be trait markers for alcoholism providing clues to brain mechanisms of vulnerability. However, it is unclear whether alpha power and coherence differences reflect reversible toxic or withdrawal effects of alcohol.

METHOD

The EEGs of 10 non-abstinent and 16 long-term abstinent alcoholics (7.7 +/- 5.8 years) and 25 controls were analyzed. Levels of anxiety and depression were assessed by questionnaire.

RESULTS

No statistically significant EEG power differences were observed between groups, although the numerical difference between alcoholics and controls was similar to that previously reported. Bilateral, intrahemispheric, posterior coherences were significantly increased in the alpha and beta frequency bands both in long-term abstinent and non-abstinent alcohol-dependent subjects - particularly when depressiveness was included as a covariate.

CONCLUSION

These results suggest that increased EEG-coherence (cortical synchronization) may serve as endophenotype for alcoholism in conjunction with increased depressiveness and point to a possible involvement of GABAergic and/or glutamatergic neurotransmission.