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PubMed2006

Lower TSH and higher T4 levels are associated with current depressive syndrome in young adults.

OBJECTIVE: The relationship of individual thyroid function indices to depression in those without a history of prior thyroid dysfunction is uncertain. METHOD: We examined the relationship between thyroid-stimulating hormone (TSH) and thyroxine (T4) levels and current or lifetime history of depressive symptoms using information from 6869 participants, aged 17-39 years, in the Third National Health and Nutrition Examination Survey without history of thyroid-related illness. RESULTS: We found that lower TSH and higher T4 levels were associated with current depressive syndrome in men, but only higher T4 levels correlated with current depressive syndrome in women. Lifetime depressive syndrome was associated with neither TSH level nor T4 levels in men or women. CONCLUSION: These findings suggest that transient or 'state dependent' changes are associated with depression in those without a history of thyroid illness. Further studies to discern whether these depression-associated changes represent distinct endophenotypes of depression should be encouraged.

Adolescent↗

PubMed2006

Candidate gene studies in the 21st century: meta-analysis, mediation, moderation.

The results of a large body of candidate gene studies of behavioural and psychiatric phenotypes have been largely inconclusive, with most findings failing to replicate reliably. A variety of approaches that augment the 'traditional' candidate gene approach are discussed, including the use of meta-analysis to combine findings from existing published reports, the investigation of mediating variables (including the use of intermediate phenotypes or endophenotypes) and the awareness of possible moderating influences (such as sex or ethnicity) and gene-environment interactions on genetic associations, possibly via epigenetic mechanisms. Advances in genotyping technology will also allow the routine use of haplotype analysis and linkage disequilibrium mapping. Examples of how these approaches may improve our understanding of how genetic associations with behavioural and psychiatric phenotypes obtain are given.

Behavior↗

PubMed2005

Interaction between the alpha-T catenin gene (VR22) and APOE in Alzheimer's disease.

BACKGROUND: APOE is the only gene that has been consistently replicated as a risk factor for late onset Alzheimer's disease. Several recent studies have identified linkage to chromosome 10 for both risk and age of onset, suggesting that this region harbours genes that influence the development of the disease. A recent study reported association between single nucleotide polymorphisms (SNPs) in the VR22 gene (CTNNA3) on chromosome 10 and plasma levels of Abeta42, an endophenotype related to Alzheimer's disease. OBJECTIVE: To assess whether polymorphisms in the VR22 gene are associated with Alzheimer's disease in a large sample of Alzheimer's disease families and an independent set of unrelated cases and controls. RESULTS: Several SNPs showed association in either the family based or case-control analyses (p<0.05). The most consistent findings were with SNP6, for which there was significant evidence of association in both the families and the unrelated cases and controls. Furthermore, there was evidence of significant interaction between APOE-4 and two of the VR22 SNPs, with the strongest evidence of association being concentrated in individuals carrying APOE-4. CONCLUSIONS: This study suggests that VR22 or a nearby gene influences susceptibility to Alzheimer's disease, and the effect is dependent on APOE status.

Aged↗

PubMed2007

The functional impact of SLC6 transporter genetic variation.

Solute carrier 6 (SLC6) is a gene family of ion-coupled plasma membrane cotransporters, including transporters of neurotransmitters, amino acids, and osmolytes that mediate the movement of their substrates into cells to facilitate or regulate synaptic transmission, neurotransmitter recycling, metabolic function, and fluid homeostasis. Polymorphisms in transporter genes may influence expression and activity of transporters and contribute to behavior, traits, and disease. Determining the relationship between the monoamine transporters and complex psychiatric disorders has been a particular challenge that is being met by evolving approaches. Elucidating the functional consequences of and interactions among polymorphic sites is advancing our understanding of this relationship. Examining the influence of environmental influences, especially early-life events, has helped bridge the gap between genotype and phenotype. Refining phenotypes, through assessment of endophenotypes, specific behavioral tasks, medication response, and brain network properties has also improved detection of the impact of genetic variation on complex behavior and disease.

Attention Deficit Disorder with Hyperactivity↗

PubMed2005

Human development: biological and genetic processes.

Adaptation is a central organizing principle throughout biology, whether we are studying species, populations, or individuals. Adaptation in biological systems occurs in response to molar and molecular environments. Thus, we would predict that genetic systems and nervous systems would be dynamic (cybernetic) in contrast to previous conceptualizations with genes and brains fixed in form and function. Questions of nature versus nurture are meaningless, and we must turn to epigenetics--the way in which biology and experience work together to enhance adaptation throughout thick and thin. Defining endophenotypes--road markers that bring us closer to the biological origins of the developmental journey--facilitates our understanding of adaptive or maladaptive processes. For human behavioral disorders such as schizophrenia and autism, the inherent plasticity of the nervous system requires a systems approach to incorporate all of the myriad epigenetic factors that can influence such outcomes.

Adaptation, Psychological↗

PubMed2003

Genetic Models in Applied Physiology. HXB/BXH rat recombinant inbred strain platform: a newly enhanced tool for cardiovascular, behavioral, and developmental genetics and genomics.

This review deals with the largest set of rat recombinant inbred (RI) strains and summarizes past and recent accomplishments with this platform for genetic mapping and analyses of divergent and complex traits. This strain, derived by crossing the spontaneously hypertensive rat, SHR/Ola, with a Brown Norway congenic, BN-Lx, carrying polydactyly-luxate syndrome, is referred to as HXB/BXH. The RI strain set has been used for linkage and association studies to identify quantitative trait loci for numerous cardiovascular phenotypes, including arterial pressure, stress-elicited heart rate, and pressor response, and metabolic traits, including insulin resistance, dyslipidemia and glucose handling, and left ventricular hypertrophy. The strain's utility has been enhanced with development of a new framework marker-based map and strain distribution patterns of polymorphic markers. Quantitative trait loci for behavioral traits mapped include loci for startle motor response and habituation, anxiety and locomotion traits associated with elevated plus maze, and conditioned taste aversion. The polydactyly-luxate syndrome Lx mutation has allowed the study of alleles important to limb development and malformation phenotypes as well as teratogens. The RI strains have guided development of numerous congenic strains to test locus assignments and to study the effect of genetic background. Although these strains were originally developed to aid in studies of rat genetic hypertension and morphogenetic abnormalities, this rodent platform has been shown to be equally powerful for a wide spectrum of traits and endophenotypes. These strains provide a ready and available vehicle for many physiological and pharmacological studies.

Animals↗

PubMed2004

Genetic dissection of learning and memory in mice.

In this minireview, we discuss different strategies to dissect genetically the keystones of learning and memory. First, we broadly sketch the neurogenetic analysis of complex traits in mice. We then discuss two general strategies to find genes affecting learning and memory: candidate gene studies and whole genome searches. Next, we briefly review more recently developed techniques, such as microarrays and RNA interference. In addition, we focus on gene-environment interactions and endophenotypes. All sections are illustrated with examples from the learning and memory field, including a table summarizing the latest information about genes that have been shown to have effects on learning and memory.

Animals↗

PubMed2004

Defining the phenotype in human genetic studies: forward genetics and reverse phenotyping.

The definition of phenotypes for genetic study is a challenging endeavor. Just as we apply strict quality standards to genotype data, we should expect that phenotypes meet consistently high standards of reproducibility and validity. The methods for achieving accurate phenotype assignment in the research setting--the 'research diagnosis'--are different from the methods used in clinical diagnosis in the patient care setting. We evaluate some of the main challenges of phenotype definition in human genetics, and begin to outline a set of standards to which phenotypes used in genetics studies may aspire with the goal of increasing the quality and reproducibility of linkage and association studies. Revisiting the traditional phenotype definitions through a focus on familial components and heritable endophenotypes is a time-honored approach. Reverse phenotyping, where phenotypes are refined based on genetic marker data, may be a promising new approach. The stakes are high, since the success of gene mapping in genetically complex disorders hinges on the ability to delineate the target phenotype with accuracy and precision.

Chromosome Mapping↗

PubMed2005

Relationship between class I and II HLA antigens in schizophrenia and eye movement disturbances: a preliminary study.

The region coding human leukocyte antigen (HLA) on chromosome 6q21 was shown to be associated with both the vulnerability to schizophrenia and presence of eye movement disturbances (EMD). The aim of this preliminary study was to investigate how individual class I and II HLA antigens in schizophrenic patients may be related to schizophrenia and to the intensity of two kinds of EMD: fixation and smooth pursuit. The incidence of HLA antigens was compared between 40 schizophrenic patients (17 male, 23 female) and 198 healthy control subjects (112 male, 86 female). In schizophrenic patients, the intensity of EMD assessed by infrared reflectometry and quantified on a scale from 0 to 3 was correlated with the incidence of HLA antigens. A number of differences regarding HLA antigens were found between schizophrenic patients and healthy subjects. Significant correlation was also obtained between some EMD and a number of HLA antigens. Antigens A24 and A28 were found to occur in different frequencies in schizophrenic patients and healthy control subjects. They also correlated with EMD on the fixation and smooth pursuit tests. The results obtained show an association between HLA antigens and EMD as an endophenotypic marker of schizophrenia, and may add to other findings on susceptibility loci for schizophrenia on chromosome 6p21. A limitation of this study is a small number of investigated patients with schizophrenia.

Adolescent↗

PubMedDate not supplied

Linkage analysis with biological markers.

Biological markers or endophenotypes may be used to help delineate the relationships between underlying trait genotypes and trait phenotypes. However, analyzing quantitative biological markers jointly with a qualitative trait phenotype (affected versus unaffected) for linkage with genetic marker loci is not straightforward. For the situation in which both the biological marker(s) and the qualitative trait phenotype are under the control of underlying genotypes, a simple method is developed for jointly using biological marker and trait phenotype in linkage analysis. An example demonstrates its implementation in the LINKAGE programs.

Biomarkers↗

PubMed1992

Are schizophrenia and affective disorder related? A selective literature review.

OBJECTIVE: Although most modern investigators accept the Kraepelinian view that schizophrenia and affective disorder are biologically distinct, others have suggested the psychoses are on a continuum of liability. This article is a selective review of evidence for the continuum model. METHOD: The author focuses on family, twin, and adoption data that do not support the Kraepelinian view of psychosis. Evidence characterized to a lesser extent includes the frequency of intermediate forms of illness (i.e., schizoaffective disorder), the inability to separate psychoses by classical symptoms into well-defined clusters, and the inability of laboratory measures to clearly define psychotic subgroups. RESULTS: The data demonstrate that schizophrenia and affective disorder do co-occur in some families. Whether this co-occurrence reflects true overlap is unclear, and significant pathophysiological heterogeneity may underlie clinical continuity. In some recent studies the inclusion of nonmelancholic depressions in the affective illness category may have masked overlap. CONCLUSIONS: The author suggests that the Kraepelinian view of psychoses may need modification. Future research should focus on factors that may reveal overlap between schizophrenia and affective disorder: severity of schizophrenia and affective disorder in probands, severity of depression in relatives, the effect of the unipolar-bipolar disorder relationship on the co-occurrence of affective disorder and schizophrenia, and the relationship of nongenetic factors that might alter the clinical expression of a shared genotype. Also, investigators should not presume a dichotomy or continuum but should examine pure and mixed pedigrees and look for state- and trait-related endophenotypes, the convergence of which would provide the basis for focused molecular genetic study.

Adult↗

PubMed2006

Episodic memory performance predicted by the 2bp deletion in exon 6 of the "alpha 7-like" nicotinic receptor subunit gene.

OBJECTIVE: There is evidence of linkage between chromosome 15q14 and the P50 auditory evoked response, a heritable neuropsychological marker associated with increased risk of schizophrenia. Chromosome 15q14 harbors the alpha-7 nicotinic receptor subunit gene (CHRNA7) and a hybrid gene of unknown function (CHRFAM7A). CHRNA7 is involved in memory formation, a core dysfunction in schizophrenia. The authors set out to determine if this locus is associated with memory dysfunction in schizophrenia. METHOD: A 2bp deletion in exon 6 of CHRFAM7A, which disrupts the hybrid gene and has previously been associated with P50 deficit, was genotyped in 251 individuals from the Maudsley Family Study of schizophrenia. Episodic memory function was assessed using the Wechsler Memory Scale. RESULTS: Significant associations were identified with delayed recall and percentage retained, with the presence of the deletion predicting worse performance. CONCLUSIONS: These observations indicate that episodic memory function is a schizophrenia endophenotype and implicate the CHRFAM7A/CHRNA7 locus in modulating its function.

Chromosome Mapping↗

PubMed2001

Saccadic disinhibition in patients with acute and remitted schizophrenia and their first-degree biological relatives.

OBJECTIVE: Performance on measures of saccadic inhibition and control was investigated in a large family study of schizophrenia to evaluate the utility of using antisaccade task performance as an endophenotypic marker of genetic liability for schizophrenia. METHOD: Ninety-five patients with acute schizophrenia and 116 of their first-degree biological relatives, 13 schizophrenia patients whose illness was in full remission, 35 patients with acute psychotic affective disorder, and 109 nonpsychiatric comparison subjects were administered antisaccade and prosaccade tasks. RESULTS: Both schizophrenia patient groups had a greater number of errors on the antisaccade task than did the first-degree relatives and the affective disorder group, which both had more errors than the comparison subjects. Among the first-degree relatives of the probands with acute schizophrenia, relatives of poor-performing patients performed worse on the antisaccade task than relatives of patients with good performance. Reflexive errors were not likely the result of interfering psychotic symptoms, medication, or medication side effects. Although the schizophrenia patients demonstrated other signs of saccadic abnormalities, these problems, which were not observed in their relatives even though they had high antisaccade error rates, seem unlikely to account for the higher antisaccade error rate of the schizophrenia patients. CONCLUSIONS: These findings suggest that saccadic disinhibition is strongly associated with the genetic liability for schizophrenia.

Acute Disease↗

PubMed2002

Comorbid bipolar disorder and panic disorder in families with a high prevalence of bipolar disorder.

OBJECTIVE: Panic attacks are a common complication of affective disorder, although the etiologic relationship of panic and affective symptoms has not been determined. Evidence from a family study suggests that panic attacks and panic disorder may be related genetically to bipolar disorder. This study used diagnostic data from the NIMH Bipolar Disorder Genetics Initiative to assess in a separate, larger family set the familiality of panic combined with bipolar disorder. METHOD: First-degree relatives (N=966) of probands with bipolar I disorder (N=192) and schizoaffective disorder, bipolar type, (N=11) were included in the study. All subjects were interviewed directly and were assigned best-estimate diagnoses for major affective and other psychiatric disorders. The risk of a family member being diagnosed with panic disorder if the proband with bipolar disorder had panic attacks or panic disorder was calculated with logistic regression analysis with generalized estimating equations that controlled for sex and affective disorder subdiagnosis. RESULTS: More than 90% of the probands and first-degree relatives with panic disorder also had an affective disorder diagnosis. Panic disorder was present in 17% of the relatives with recurrent major affective disorder and in 3% of the relatives without recurrent major affective disorder. Risk of panic disorder in relatives with bipolar disorder was increased significantly if the proband had panic attacks or panic disorder. CONCLUSIONS: Risk for panic disorder with familial bipolar disorder appears to be inherited. Inherited risk for panic disorder with bipolar disorder may indicate a shared genetic etiology for both disorders in some families. The patterns of bipolar disorder and panic disorder comorbidity observed in families imply a complex genetic etiology, which may be elucidated by using endophenotypes.

Adult↗

PubMed2002

Are cognitive impairments associated with sensitivity to stress in schizophrenia? An experience sampling study.

OBJECTIVE: Patients with a diagnosis of schizophrenia display cognitive impairments and abnormal sensitivity to stress. However, little is known about the relationship between these two endophenotypes. METHOD: Neuropsychological tests were administered to 42 patients with schizophrenia or other psychosis to assess cognitive functioning, and the experience sampling method (a structured diary technique assessing current context and mood in daily life) was used to assess 1) appraised subjective stress related to daily events and activities and 2) emotional reaction to these daily life stressors. RESULTS: Multilevel random regression analyses showed that in some instances, cognitive functioning did not alter emotional reaction to stress. In other instances, an inverse relationship was found, indicating that a better performance on neuropsychological tests was related to greater emotional reaction to stress. CONCLUSIONS: The results indicate that emotional reaction to stress in the daily lives of patients with schizophrenia may not be a consequence of cognitive impairments and that the two mechanisms may act through different pathways. Such pathways may be related to the extremes of clinical outcome that have been observed in schizophrenia: an episodic, reactive, good outcome and a more chronic form characterized by high levels of negative symptoms and cognitive impairments.

Adult↗

PubMed2003

Protective association of genetic variation in alcohol dehydrogenase with alcohol dependence in Native American Mission Indians.

OBJECTIVE: Two alcohol dehydrogenase genes (ADH2 and ADH3 on chromosome 4) and one aldehyde dehydrogenase gene (ALDH2 on chromosome 12) exhibit functional polymorphisms. The goal of this study was to determine whether any associations exist between the ADH2, ADH3, and ALDH2 polymorphisms and alcohol dependence in a group of Native Americans. An additional goal was to determine if any associations exist between these polymorphisms and the endophenotype, maximum number of drinks ever consumed in a 24-hour period. METHOD: Mission Indian adults (N=340) were recruited for participation from reservations in southern California. Each participant completed an interview with the Semi-Structured Assessment for the Genetics of Alcoholism. A blood sample was collected from each participant for genotyping at the ALDH2, ADH2, and ADH3 loci. RESULTS: Sixty percent of all participants (72% of men and 53% of women) met lifetime DSM-III-R criteria for alcohol dependence. A significant difference in the ADH2 allele distributions was found between alcohol-dependent and non-alcohol-dependent participants. Those with alcohol dependence were significantly less likely to have the ADH2*3 allele (odds ratio=0.28) and significantly more likely to have the ADH2*1 allele (odds ratio=2.00) than those who were not alcohol dependent. Individuals with ADH2*3 reported a lower number of maximum drinks ever consumed in a 24-hour period, compared to those without this allele. CONCLUSIONS: These results are consistent with genetic linkage studies showing protective associations for alcohol dependence and related behavior on chromosome 4 and suggest that ADH2 polymorphisms may account for these findings. These results also highlight the utility of evaluating protective factors in populations with high rates of alcohol dependence.

Adolescent↗

PubMed2003

Deficits in gain of smooth pursuit eye movements in schizophrenia and affective disorder patients and their unaffected relatives.

OBJECTIVE: Disturbance of smooth pursuit eye movements has been discussed as marking a putative endophenotype closely associated with the genetic basis of schizophrenia. Previous studies are not conclusive in regard to the specificity of this marker. Therefore, oculomotor pursuit was evaluated in unaffected family members of index probands diagnosed as having either schizophrenia or affective disorders. METHOD: A series of eye tracking tasks were performed by 54 patients with schizophrenia or schizoaffective disorder, 46 patients with an affective disorder, 43 unaffected first-degree relatives of the schizophrenia patients, 36 unaffected first-degree relatives of the affective disorder patients, and 84 healthy comparison subjects. The gain, which relates the velocity of the eye movement to the velocity of the target, was determined to index the intactness of the oculomotor pursuit system. RESULTS: Mean pursuit gain was significantly lower in the schizophrenia and affective disorder patients than in the healthy comparison subjects. Moreover, the relatives of both the schizophrenia and affective disorder patients showed significant gain deficits of about one-half the size of those observed in the patients. CONCLUSIONS: Gain deficits are present in psychotic patients and in their unaffected biological relatives. This finding supports a genetic origin of eye tracking disturbances in major psychotic disorders. There is no evidence for diagnostic or familial specificity. The weak sensitivity of the marker suggests that it refers to a nonnecessary genetic factor in schizophrenic and affective disorders.

Adolescent↗

PubMed2004

Medial prefrontal cortex activity associated with symptom provocation in eating disorders.

OBJECTIVE: The authors sought to identify neural correlates of eating disorders in order to contribute to the debate on the genesis and classification of eating disorders and provide endophenotypes for genetic research. METHOD: Twenty-six female patients with eating disorders (10 with bulimia nervosa, 16 with anorexia nervosa) and 19 healthy female comparison subjects matched for age and education were presented with food and aversive emotional images while brain activity was recorded with functional magnetic resonance imaging. RESULTS: Women with eating disorders identified the food stimuli as threatening and disgusting. In response to these stimuli, the women with eating disorders had greater activation in the left medial orbitofrontal and anterior cingulate cortices and less activation in the lateral prefrontal cortex, inferior parietal lobule, and cerebellum, relative to the comparison group. In addition, women with bulimia nervosa had less activation in the lateral and apical prefrontal cortex, relative to the comparison group. Between-group differences in response to nonspecific emotional stimuli were found in the occipital cortex, parietal cortex, and cerebellum. CONCLUSIONS: A medial prefrontal response to symptom-provoking stimuli was identified as a common feature of anorexia and bulimia nervosa. This finding supports a conceptualization of eating disorders as being transdiagnostic at the neural level. The abnormal prefrontal reaction is associated with symptom-related material, whereas the occipital and cerebellar differences are nonspecific. An abnormal propensity to activate medial prefrontal circuits in response to inappropriate stimuli is common to eating, obsessive-compulsive, and addictive disorders and may account for the compulsive features of behavior in these conditions.

Adult↗