Association between 5-HT(2A) receptor polymorphism and psychotic symptoms in Alzheimer's disease

Exploring the Genetic Landscape of Mild Behavioral Impairment as an Early Marker of Cognitive Decline: An Updated Review Focusing on Alzheimer's Disease

The clinical features and pathophysiology of neuropsychiatric symptoms (NPSs) in dementia have been extensively studied. However, the genetic architecture and underlying neurobiological mechanisms of NPSs at preclinical stages of cognitive decline and Alzheimer's disease (AD) remain largely unknown. Mild behavioral impairment (MBI) represents an at-risk state for incident cognitive impairment and is defined by the emergence of persistent NPSs among non-demented individuals in later life. These NPSs include affective dysregulation, decreased motivation, impulse dyscontrol, abnormal perception and thought content, and social inappropriateness. Accumulating evidence has recently begun to shed more light on the genetic background of MBI, focusing on its potential association with genetic factors related to AD. The Apolipoprotein E (APOE) genotype and the MS4A locus have been associated with affective dysregulation, ZCWPW1 with social inappropriateness and psychosis, BIN1 and EPHA1 with psychosis, and NME8 with apathy. The association between MBI and polygenic risk scores (PRSs) in terms of AD dementia has been also explored. Potential implicated mechanisms include neuroinflammation, synaptic dysfunction, epigenetic modifications, oxidative stress responses, proteosomal impairment, and abnormal immune responses. In this review, we summarize and critically discuss the available evidence on the genetic background of MBI with an emphasis on AD, aiming to gain insights into the potential underlying neurobiological mechanisms, which till now remain largely unexplored. In addition, we propose future areas of research in this emerging field, with the aim to better understand the molecular pathophysiology of MBI and its genetic links with cognitive decline.

Neuropsychiatric Symptoms of Alzheimer's Disease: An Anatomic-Genetic Framework for Treatment Development

BACKGROUND

Despite the burden on patients and caregivers, there are no approved therapies for the neuropsychiatric symptoms of Alzheimer's disease (NPS-AD). This is likely due to an incomplete understanding of the underlying mechanisms.

OBJECTIVE

To review the neurobiological mechanisms of NPS-AD, including depression, psychosis, and agitation.

METHODS

Understanding that genetic encoding gives rise to the function of neural circuits specific to behavior, we review the genetics and neuroimaging literature to better understand the biological underpinnings of depression, psychosis, and agitation.

RESULTS

We found that mechanisms involving monoaminergic biosynthesis and function are likely key elements of NPS-AD and while current treatment approaches are in line with this, the lack of effectiveness may be due to contributions from additional mechanisms including neurodegenerative, vascular, inflammatory, and immunologic pathways.

CONCLUSION

Within an anatomic-genetic framework, development of novel effective biological targets may engage targets within these pathways but will require a better understanding of the heterogeneity in NPS-AD.

The Association between 5HT2A T102C and Behavioral and Psychological Symptoms of Dementia in Alzheimer's Disease: A Meta-Analysis

The serotonin receptor gene (5-HT2A) has been reported to be a susceptible factor in behavioral and psychological symptoms of dementia (BPSD) in Alzheimer's disease (AD). However, previous results were conflicting. We aim to investigate the association of 5-HT2A T102C with BPSD in AD using a meta-analysis. Studies were collected using PubMed, Web of Science, the Cochrane Library databases, Chinese National Knowledge Infrastructure (CNKI), and Embase. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess associations. Nine studies with 1899 AD patients with/without BPSD were included in this meta-analysis. The 102C and CC genotypes were associated with psychosis in AD (102C: p < 0.00001, OR [95% CI] = 3.19 [2.12-4.79]; CC: p < 0.00001, OR [95% CI] = 7.24 [3.60-14.59]). The TT genotype was significantly associated with hallucinations, aberrant motor behavior, and psychosis in AD (hallucinations: p = 0.001, OR [95% CI] = 0.52 [0.36-0.77]; aberrant motor behavior: p = 0.03, OR [95% CI] = 0.58 [0.35-0.95]; and psychosis: p = 0.002, OR [95% CI] = 0.34 [0.17-0.67]). No association was observed between T102C alleles or genotypes and delusions, agitation/aggression, depression, and apathy (p > 0.05). Thus, the 5HT2A T102C might be a susceptible factor for hallucinations, aberrant motor behavior, and psychosis in AD. The potential mechanism of this polymorphism in BPSD in AD requires further exploration.

Genetics of psychosis of Alzheimer disease

Psychotic symptoms, comprised of delusions and hallucinations, occur in about half of individuals with Alzheimer disease (AD with psychosis, AD+P). These individuals have greater agitation, aggression, depression, functional impairment, and mortality than individuals without psychosis (AD-P). Although the exact etiopathogenesis of AD+P is unclear, the rapidly developing field of genomics continues to expand our understanding of this disease. Several independent studies have demonstrated familial aggregation and heritability of AD+P. Linkage studies have been suggestive of loci on several chromosomes associated with AD+P. Association studies examining apolipoprotein E gene, the best established genetic risk factor for late-onset AD, did not find any significant association of this gene with AD+P. Other candidate gene studies focusing on monoamine neurotransmitter systems have yielded equivocal results. A genome-wide association study and studies examining copy number variations recently have detected suggestive associations, but have been underpowered. Approaches to increase sizes of AD+P samples for genome wide association studies are discussed. © 2016 Wiley Periodicals, Inc.

Ascending monoaminergic systems alterations in Alzheimer's disease. translating basic science into clinical care

Extensive neuropathological studies have established a compelling link between abnormalities in structure and function of subcortical monoaminergic (MA-ergic) systems and the pathophysiology of Alzheimer's disease (AD). The main cell populations of these systems including the locus coeruleus, the raphe nuclei, and the tuberomamillary nucleus undergo significant degeneration in AD, thereby depriving the hippocampal and cortical neurons from their critical modulatory influence. These studies have been complemented by genome wide association studies linking polymorphisms in key genes involved in the MA-ergic systems and particular behavioral abnormalities in AD. Importantly, several recent studies have shown that improvement of the MA-ergic systems can both restore cognitive function and reduce AD-related pathology in animal models of neurodegeneration. This review aims to explore the link between abnormalities in the MA-ergic systems and AD symptomatology as well as the therapeutic strategies targeting these systems. Furthermore, we will examine possible mechanisms behind basic vulnerability of MA-ergic neurons in AD.

Cannabinoid receptor agonists upregulate and enhance serotonin 2A (5-HT(2A)) receptor activity via ERK1/2 signaling

Recent behavioral studies suggest that nonselective agonists of cannabinoid receptors may regulate serotonin 2A (5-HT(2A)) receptor neurotransmission. Two cannabinoids receptors are found in brain, CB1 and CB2 receptors, but the molecular mechanism by which cannabinoid receptors would regulate 5-HT(2A) receptor neurotransmission remains unknown. Interestingly, we have recently found that certain cannabinoid receptor agonists can specifically upregulate 5-HT(2A) receptors. Here, we present experimental evidence that rats treated with a nonselective cannabinoid receptor agonist (CP 55,940, 50 µg/kg, 7 days) showed increases in 5-HT(2A) receptor protein levels, 5-HT(2A) receptor mRNA levels, and 5-HT(2A) receptor-mediated phospholipase C beta (PLCβ) activity in prefrontal cortex (PFCx). Similar effects were found in neuronal cultured cells treated with CP 55,940 but these effects were prevented by selective CB2, but not selective CB1, receptor antagonists. CB2 receptors couple to the extracellular kinase (ERK) signaling pathway by Gα(i/o) class of G-proteins. Noteworthy, GP 1a (selective CB2 receptor agonist) produced a strong upregulation of 5-HT(2A) receptor mRNA and protein, an effect that was prevented by selective CB2 receptor antagonists and by an ERK1/2 inhibitor, PD 198306. In summary, our results identified a strong cannabinoid-induced upregulation of 5-HT(2A) receptor signaling in rat PFCx. Our cultured cell studies suggest that selective CB2 receptor agonists upregulate 5-HT(2A) receptor signaling by activation of the ERK1/2 signaling pathway. Activity of cortical 5-HT(2A) receptors has been associated with several physiological functions and neuropsychiatric disorders such as stress response, anxiety and depression, and schizophrenia. Therefore, these results may provide a molecular mechanism by which activation of cannabinoid receptors might be relevant to the pathophysiology of some cognitive and mood disorders in humans.

Missense substitutions associated with behavioural disturbances in Alzheimer's disease (AD)

Behavioural and psychological symptoms in dementia, or BPSD, occur in the majority of Alzheimer's disease (AD) patients. They are associated with considerable patient morbidity and greater care-giver stress. There is some evidence suggesting that BPSD have a genetic component and a large number of studies have examined the association of candidate genes with these symptoms. This review provides a comprehensive summary of all the published studies investigating the association of candidate gene missense substitutions with BPSD. Missense substitutions could potentially alter protein function or render the protein non-functional, resulting in phenotypic consequences. More than 80 studies investigating the association of 8 missense substitutions in 7 genes with BPSD were identified. However, results of these studies are contradictory and do not provide firm support for these associations. Larger studies and more systematic approaches will delineate the association of missense substitutions with behavioural symptoms in AD.

Apolipoprotein E genotypes and neuropsychiatric symptoms and syndromes in late-onset Alzheimer's disease

Neuropsychiatric symptoms (NPS) in dementia, previously denominated as behavioural and psychological symptoms of dementia, are often more distressing, impairing, and costly than cognitive symptoms, representing a major health burden for older adults. These symptoms are common features of Alzheimer's disease (AD), and are one of the major risk factors for institutionalization. There is a high prevalence of neuropsychiatric disturbances in patients with AD, including depression, anxiety, apathy, psychosis, aggression, and agitation. At present, the role of the apolipoprotein E (APOE) genotypes in the development of NPS or neuropsychiatric syndromes/endophenotypes in AD patients is unclear. In this article, we summarized the findings of the studies of NPS and neuropsychiatric syndromes in AD in relation to APOE genotypes, with special attention to the possible underlying mechanisms. While some studies failed to find a significant association between the APOE polymorphism and NPS in late-onset AD, other studies reported a significant association between the APOE ɛ4 allele and an increase in agitation/aggression, hallucinations, delusions, and late-life depression or anxiety. However, current cumulative evidence coming from the few existing longitudinal studies shows no association of APOE genotypes with NPS as a whole in AD. Some negative studies that focused on the distribution of APOE genotypes between AD patients with or without NPS further emphasized the importance of sub-grouping NPS in distinct neuropsychiatric syndromes. Explanations for the variable findings in the existing studies included differences in patient populations, differences in the assessment of neuropsychiatric symptomatology, possible lack of statistical power to detect associations in the negative studies, and small sample sizes generating false positives that cannot be consistently replicated. Finally, many reviewed studies were cross-sectional, whereas it would be of paramount importance to evaluate the risk for incident NPS in relation to the APOE genotype in prospectively followed cohorts of AD patients. In fact, identifying predisposing genetic risk factors may allow us to understand the pathophysiological features of neuropsychiatric syndromes or symptoms in AD, so optimizing possible therapeutic options.

Neuropsychiatric Symptoms, Endophenotypes, and Syndromes in Late-Onset Alzheimer's Disease: Focus on APOE Gene

Neuropsychiatric symptoms, previously denominated as behavioural and psychological symptoms of dementia, are common features of Alzheimer's disease (AD) and are one of the major risk factors for institutionalization. At present, the role of the apolipoprotein E (APOE) gene in the development of neuropsychiatric symptoms in AD patients is unclear. In this paper, we summarized the findings of the studies of neuropsychiatric symptoms and neuropsychiatric syndromes/endophenotypes in AD in relation to APOE genotypes, with special attention to the possible underlying mechanisms. While some studies failed to find a significant association between APOE and neuropsychiatric symptoms in late-onset AD, other studies reported a significant association between the APOE ε4 allele and an increase in agitation/aggression, hallucinations, delusions, and late-life depression or anxiety. Furthermore, some negative studies that focused on the distribution of APOE genotypes between AD patients with or without neuropsychiatric symptoms further emphasized the importance of subgrouping neuropsychiatric symptoms in distinct neuropsychiatric syndromes. Explanations for the variable findings in the existing studies included differences in patient populations, differences in the assessment of neuropsychiatric symptomatology, and possible lack of statistical power to detect associations in the negative studies.

Behavioural genetics of Alzheimer's disease: a comprehensive review

Behavioural and psychological symptoms of dementia (BPSD) are present in the course of the illness in up to 90% of patients with Alzheimer's disease (AD). They are the main source of caregiver burden and one of the major factors contributing to early institutionalization. The involvement of a genetic component in BPSD aetiology seems beyond controversy, though the exact significance of particular polymorphisms is uncertain in the majority of cases. Multiple genes have been assessed for their putative influence on BPSD risk. In this paper we review the behavioural genetics of AD, particularly the importance, with respect to BPSD risk, of genes coding for apolipoprotein E and proteins involved in the process of neurotransmission: serotonin receptors, serotonin transporter, COMT, MAO-A, tryptophan hydroxylase and dopamine receptors. A general conclusion is the striking inconsistency of the findings, unsurprising in the field of psychiatric genetics. The potential reasons for such discrepancy are exhaustively discussed.

Genetics of psychosis in Alzheimer's disease: a review

In and of itself, late-onset Alzheimer's disease (AD) can be a devastating illness. However, a sub-group of AD patients develop psychosis as the disease progresses. These patients have an added burden of greater cognitive impairment, higher rates of institutionalization, and higher mortality than AD patients without psychosis. While the etiopathogenesis such as psychosis in AD (AD+P) is not known, mounting evidence accrued over the past ten years indicates that AD+P represents a distinct phenotype with a genetic basis. Elucidating the genetic mechanism of AD+P is crucial if better pharmaceutical treatments are to be developed for these patients. The goal of this review is to summarize what is currently known regarding the genetic basis of psychosis in AD. Specific attention is given to familial aggregation and heritability, linkage to chromosomal loci, and associations of candidate genes of APOE and the monoamine neurotransmitter system.

Serotonergic system genes in psychosis of Alzheimer dementia: meta-analysis

OBJECTIVE

The authors attempted to understand the role of two serotonin system genes, HTR2A and SLC6A4, on psychosis associated with Alzheimer dementia (AD).

METHOD

Relevant published studies were assessed, and their data were meta-analyzed to determine pooled odds ratios (ORs) that were assessed for heterogeneity. Additional robustness checks were performed to assess for publication bias and any undue influence from a single study. Finally, the number of studies required to invalidate positive findings was determined.

RESULTS

The C allele of HTR2A emerged as a significant risk factor for psychosis, with an allelic OR of 2.191 that increased to 5.143 for the homozygous CC genotype. The SLC6A4 polymorphism was not reliably associated with either psychosis or delusions.

CONCLUSIONS

The strong and robust positive association that was noted between the C allele of HTR2A and psychosis suggests that the HTR2A T102C polymorphism is a significant risk factor for psychosis of AD.

Prediction of psychosis onset in Alzheimer disease: the role of depression symptom severity and the HTR2A T102C polymorphism

Psychotic symptoms in Alzheimer disease (AD + P) identify a heritable phenotype associated with a more severe course. We recently found an association of AD + P with depression symptom severity. Reports have shown an association of a serotonin-2A receptor (HTR2A) gene T102C polymorphism with AD + P and with depression during AD. We examined the interaction of this common genetic polymorphism with depression and increased psychosis risk. Subjects with possible or probable AD or mild cognitive impairment (MCI) without psychosis at study entry were genotyped for the HTR2A T102C polymorphism and reassessed every 6 months until psychosis onset. Psychotic and depressive symptoms were rated using the CERAD behavioral rating scale (CBRS). Cox proportional hazard models with time-dependent covariates were used to examine associations with psychosis onset. A total of 324 Caucasian subjects completed at least one follow-up exam. Depressive symptom severity was a strong predictor of psychosis onset. Neither psychosis onset nor depression severity was associated with the HTR2A genotype. Genotype interacted with depression severity to moderate the risk of AD + P onset. This did not result from an interaction of HTR2A genotype with antidepressant use. Psychosis onset in AD is strongly associated with severity of depressive symptoms, an association that may be modified by HTR2A genotype.

A review of the literature on neuroimaging of serotoninergic function in Alzheimer's disease and related disorders

Behavioural and psychological disorders are frequent not only in frontotemporal dementia (FTD), but also in Alzheimer's disease (AD), and many of them are related to serotoninergic dysfunction. In vitro biochemical measurements on brain samples show both pre- and post-synaptic impaired brain serotoninergic function in degenerative dementia, sometimes related to hyperactivity or aggressive behaviour. To date, few studies have explored in vivo 5HT2A and 5HT1A brain receptors in AD and FTD. They suggest that brain cells are lost in the associative cortices (5HT2A) and hippocampus (5HT1A) of AD patients, and in the medial prefrontal and orbitofrontal cortices of FTD subjects (5HT2A). Apart from reflecting a loss of local neurons, the meaning of the decrease in 5HT receptors is not yet clear and larger populations are required to establish relationships with clinical symptoms such as dementia severity and search for possible consequences for patients' behavioural and affective status.

Analysis of the 5HT-2A T102C receptor polymorphism and psychotic symptoms in Alzheimer's disease

Although the aetiology of psychotic symptoms in Alzheimer's disease (AD) is multi-factorial, alterations in serotonergic neurotransmission are often implicated. Polymorphisms of the serotonin receptor 5HT-2A are associated with hallucinatory symptoms and delusions in demented and non-demented cohorts. This study examined the role of the 5HT-2A T102C polymorphism in influencing psychotic symptoms in a large Northern Ireland AD population (n = 406, mean MMSE 13/30). Forty-eight percent of patients experienced delusional symptoms and 28% experienced hallucinations during the course of their dementia. No significant association was found either in frequency of genotype or allelic variation for either set of symptoms. Furthermore, the mean delusional and hallucinatory severity scores did not differ significantly among the three genotype groups. The lack of influence of the T102C polymorphism of the 5HT-2A receptor on the emergence of psychotic symptoms in AD contrasts with previous reports in other cohorts involving smaller numbers of subjects.

Monoallelic and unequal allelic expression of the HTR2A gene in human brain and peripheral lymphocytes

BACKGROUND

The 102T/C polymorphism of the serotonin 2A receptor (HTR2A) gene is reported to be associated with schizophrenia and other diseases and phenotypes. Altered HTR2A expression has been found in relation to several neuropsychiatric conditions, including depression and schizophrenia. Studies of expression of HTR2A messenger RNA (mRNA) and protein in postmortem brains suggest that the 102C allele might be less transcriptionally active than the T allele. However, equal expression of both alleles has also been reported.

METHODS

We performed primer extension assays to measure relative expression of allele-specific HTR2A transcripts in mRNAs isolated from the prefrontal cortex of 31 individuals with schizophrenia and from peripheral lymphocytes (PBLs) of 31 healthy individuals heterozygous for 102T/C. We also examined the allele transmission pattern of HTR2A in PBLs of nine families.

RESULTS

Analyses of DNA and mRNA revealed that 102C is expressed but at lower levels than 102T in brains. In contrast to the biallelic expression observed in brains, monoallelic expression of HTR2A was common in PBLs. However, a family study revealed that imprinting was not responsible for the monoallelic expression in PBLs.

CONCLUSIONS

The present study revealed a tissue-specific modification of HTR2A expression, which makes allelic and epiallelic analyses necessary for genetic epidemiologic and pharmacogenomic studies of HTR2A.

Role of 5HT 2A and 5HT 2C polymorphisms in behavioural and psychological symptoms of Alzheimer's disease

OBJECTIVE

Alzheimer's disease (AD) patients suffer from behavioural and psychological symptoms of dementia (BPSD). A genetic component to BPSD development in AD has been demonstrated. Polymorphisms within serotonin receptors 5HT(2A) and 5HT(2C) have been previously investigated in a few interesting studies reviewed here, however, their role remains unclear.

METHODS

Our large cohort of 394 patients had longitudinal information on the BPSD (Neuropsychiatric Inventory), which was used to dichotomise patients into whether they had ever suffered from a given symptom within the study period and give each patient a severity score. These measures were related to the 5HT(2A) T102C and 5HT(2C) cys23ser genotype and allele frequencies.

RESULTS

Our data supports previous reports of an increased frequency of the C allele and CC genotype of the T102C variant of 5HT(2A) with hallucinations, delusions, psychosis and aberrant motor behaviour, however, we dispute previous associations with depression and aggression. We describe for the first time an increase in the C allele and CC genotype frequencies of the cys23ser variant of 5HT(2C) with anxiety and support previous associations with appetite disturbances in females.

CONCLUSION

This review and extension of previous data presents support for the role of 5HT(2A) and 5HT(2C) in the development of certain symptoms, although the effect size may be small.

The neurobiology of neuropsychiatric syndromes in dementia

PURPOSE OF REVIEW

Neuropsychiatric disturbances in dementia are prevalent, and research is uncovering their neurobiological correlates.

RECENT FINDINGS

Late-onset depression appears to be associated with Alzheimer's disease pathology at autopsy, and lifetime depression episodes may worsen Alzheimer's disease pathology in the hippocampus. Vascular disease and elevated homocysteine increase risk for both late-onset depression and Alzheimer's disease and may partly mediate their relationship. Monoamine changes are robust finding in Alzheimer's disease and may account for many observed depression symptoms. Risk of psychosis of Alzheimer's disease appears to be increased by several genes also implicated in schizophrenia (e.g., catechol-O-methyltransferase, neuregulin-1). Psychosis in dementia with Lewy bodies appears to be related to cholinergic deficits. Alzheimer's disease is associated with changes in the circadian sleep-wake cycles, including decreased night-time melatonin. Sleep apnea may be related to apolipoprotein E genotype and impact cognition in Alzheimer's disease. Rapid eye movement sleep behavior disorder is intricately related to synucleinopathies, such as dementia with Lewy bodies, but synuclein changes may not totally explain this relationship.

SUMMARY

Neuropsychiatric disturbances are a core feature of dementia and worsen many clinical outcomes. Among the most validated syndromes are depression, psychosis, and sleep disturbance of Alzheimer's disease. Neuropathology, neuroimaging, and genetic studies increasingly provide insight into the origins of these psychiatric symptoms in dementia.

Prediction of psychosis onset in Alzheimer disease: The role of cognitive impairment, depressive symptoms, and further evidence for psychosis subtypes

BACKGROUND

Psychotic symptoms in Alzheimer disease (AD+P) identify a heritable phenotype associated with more rapid cognitive decline. The authors have proposed that AD+P is itself a composite of a misidentification and a paranoid subtype with increased cognitive impairment restricted to the misidentification type. Most prior studies of the clinical correlates of AD+P have been limited, however, by the inclusion of prevalent cases.

METHODS

Subjects with possible or probable AD or mild cognitive impairment (MCI) without psychosis at study entry were assessed at the time of initial presentation and then annually. Psychotic symptoms were assessed using the CERAD Behavioral Rating Scale. Survival analyses used Cox proportional hazard models with time-dependent covariates to examine the predictors of psychosis onset.

RESULTS

A total of 288 subjects completed at least one follow-up examination. Mean duration of follow-up was 22.1 months. The incidence of psychosis was 0.19 per person-year. Cognitive impairment was associated with onset of psychosis, largely as a result of its association with onset of the misidentification, but not the paranoid, subtype. Including psychotropic medication use in the model revealed an association of antidepressant use with the onset of psychosis. This latter association appeared to arise from an underlying association between depression and the risk of psychosis onset rather than from antidepressant treatment.

CONCLUSION

These findings are consistent with the hypothesis that the misidentification and the paranoid subtypes each define a more biologically homogeneous group than AD+P as a whole. Further exploration of the relationship between depressive symptoms and psychosis in patients with AD is warranted.

Treatments for behavioural disorders in neurodegenerative diseases: drug development strategies

Neuropsychiatric symptoms and behavioural alterations are common in neurodegenerative diseases, and effective treatment of these changes represents an important unmet public health need. Imaging, neuropathological, neurotransmitter and molecular genetic studies increasingly identify specific mechanisms that mediate behavioural changes in neurodegenerative disorders and provide a platform for seeking effective therapeutic interventions. Measuring behavioural outcomes in clinical trials of antidementia agents represents an important means of evaluating treatment effectiveness, and clinical trial methodologies and behavioural instrumentation are evolving to facilitate drug development in this important therapeutic target area.

Stigmatization in Alzheimer's disease research on African American elders

Stigmatization in research sustains the spread of the silent epidemic of Alzheimer's disease (AD) in African American populations. Researchers use stereotypes and inappropriate assumptions to select a paradigm to examine the symptoms of AD. This paradigm fails to encompass the symptoms as manifested by African American elders. Yet, stigmatization can be minimized by recognizing the genetic heterogeneity of the symptoms within the general population, especially those manifested by African American elders. Thus, researchers can utilize pioneering genetic analyses to identify other paradigms critical in the assessment and proactive treatment of the symptoms of AD needed for this vulnerable population.

Behavioural changes and psychological symptoms in dementia disorders

The traditional view of dementia is that the features most important to accurate diagnosis and management are cognitive decline and functional disability. Behavioural and psychological symptoms have generally been thought to be of secondary importance, but new evidence suggests that these are important determinants of patients' distress, carer burden, and outcome in dementia; they can also be valuable diagnostic pointers to the underlying pathological cause and disease diagnosis. Better methods to detect and measure the severity of behavioural and psychological symptoms are needed and these could be used in well-designed intervention trials. Although pharmacological management is a commonly used option, it is often limited in its effects and can be associated with a substantial risk of side-effects. Progress in understanding the pathophysiological mechanisms underpinning behavioural and psychological symptoms in dementia will assist in developing more effective treatment approaches.

HTR2A: association and expression studies in neuropsychiatric genetics

Over the last decade the gene encoding 5-hydroxytryptamine (serotonin) receptor 2A (HTR2A) has been implicated as a functional candidate in many neuropsychiatric phenotypes including: schizophrenia, attention deficit hyperactivity disorder (ADHD), affective disorders, eating disorders, anxiety disorders, obsessive-compulsive disorder, suicide and Alzheimer's disease (AD). Different studies have tested for genetic association (case-control and family-based studies), protein expression (receptor binding assays), transcriptional expression (mRNA assays) and allelic expression. In this review we examine and summarize these findings in various neuropsychiatric phenotypes.

Psychotic symptoms in Alzheimer’s disease are not influenced by polymorphic variation at the dopamine receptor DRD3 gene

It has been suggested that genetic influences unmasked during neurodevelopment to produce schizophrenia may appear throughout neurodegeneration to produce AD plus psychosis. Risk of schizophrenia and psychosis in Alzheimer's disease (AD) has been linked to polymorphic variation at the dopamine receptor DRD3 gene implying similar causative mechanisms. We tested this association in a large cohort of Alzheimer's disease patients with a diagnosis of probable AD of 3 years or more duration from the relatively genetically homogenous Northern Irish population. We assessed relationships between genotypes/alleles of the DRD3 BalI polymorphism and the presence or absence of psychotic symptoms (delusions, hallucinations) in AD patients during the month prior to interview and at any stage during the dementia. No significant associations were found when delusions and hallucinations were cross-tabulated against S and G alleles and SS, SG and GG genotypes. Logistic regression failed to detect any influence of APOE, gender, family history or prior psychiatric history. In conclusion, we were unable to confirm previously reported associations between the DRD3 BalI polymorphism and psychotic symptoms in AD.

Serotonergic polymorphisms and psychotic disorders in populations from North Spain

There is strong biological evidence relating alterations in the serotonergic system with mental disorders. These alterations may be originated at the DNA level by sequence mutations that alter the functioning of serotonin receptors and transporter. To test this hypothesis we investigated three genetic variants of the 5-HT2A receptor (-1438G/A, 102T/C and His452Tyr) and two variants of the serotonin transporter (a VNTR in the second intron and a 44 bp insertion/delition in the promoter region of the gene) in a clinical sample recruited in a human isolate and in surrounding areas in Northern Spain (N = 257) and in ethnically matched controls (N = 334). No clear association was found between 5-HT2A variants and psychosis. However, marginal associations were observed between the 5-HTT LPR and VNTR variants and psychosis (P < or = 0.05) indicating a minor contribution to psychosis of genetic alterations in this gene.

Hallucinations et démences

Hallucinations are a common feature of certain degenerative diseases with a risk of dementia such as Alzheimer's disease, Lewy body dementia, and Parkinson's disease. Obtaining valid epidemiological data is nevertheless quite difficult because of methodological problems. As a rule, hallucinations are more prevalent in Lewy body disease than Parkinson's disease or Alzheimer's disease. The prevalence in parkinsonian dementia is about the same as in Lewy body disease. Complex visual hallucinations predominate, auditory or tactile hallucinations are more exceptional. Minor forms (illusions, sensation of presence) are also observed. Recurrence is common, mainly in the evening or at night. Patients with advanced mental impairment generally take the hallucinations for reality. The hallucinations can be associated with psychological and behavioral disorders such as delusionnal idea or identification disorders. It is important to search for other causes of hallucinations such as drugs, ocular disorders, or depression, but many of these disorders are common comorbidities in elderly patients with degenerative disease. There is no unique model fitting all the hypothesized pathogenic mechanisms. Complex visual hallucinations most likely arise from abnormal activation of the extra-striat temporal associative regions, but only hypothetical mechanisms have been proposed. Genetic studies and functional imaging have not provided convincing evidence. Current focus is placed on an imbalance between deficient cholinergic transmission and preserved or augmented monoaminergic transmission at the cortical level, but other neurotransmission systems could be involved. The dream dysregulation mechanism proposed in Parkinson's disease cannot be generalized. The link between cognitive disorders and hallucination is also poorly understood: hallucinations are associated with more severe cognitive impairments or more rapid cognitive deline in Parkinson's disease and Alzheimer's disease, but the association with specific cognitive disorders remains to be fully explored.

Review of delusions in dementia

Although delusions are common symptoms in dementia and are associated with a number of adverse outcomes, research in this area has been limited. This article attempts to summarize the existing literature on delusions in dementia with respect to known risk factors, etiology, pathogenesis, neurocognitive findings, behavioral symptoms, and treatment. This study reviews all relevant abstracts and articles pertaining to delusions and dementia. The reviewers found that the studies were limited by confusion concerning phenomenology. However, consistent findings show that delusions are associated with certain demographic variables, neuropathologic and neurocognitive findings, adverse behavioral outcomes, and limited treatment response. The authors conclude that further longitudinal studies with better clarification of terminology are required to clarify inconsistencies and shed light on future treatment options.

Serotoninergic Polymorphisms (5-HTTLPR and 5-HT2A): Association Studies with Psychosis in Alzheimer Disease

Patients with Alzheimer disease (AD) often exhibit psychotic symptoms associated with cognitive impairment. A few association studies have been carried out to determine if the serotonin transporter and receptor genes are potential risk factors for AD and/or associated psychopathology. The aim of this study was to investigate the association of a serotonin transporter gene-linked polymorphic region (5-HTTLPR) and the 5-HT2A receptor T102C polymorphism with the risk of developing dementia and/or psychotic symptoms in a group of sporadic AD patients from Italy. No significant differences in the distribution of allele and genotype frequencies of 5-HTTLPR and 5-HT2A T102C were found between patient and control groups. However, a significant association between the C102/C102 5-HT2A genotype and psychotic symptoms (p < 0.001) was observed. Our data strongly confirm results from previous studies suggesting that the C102 allele of the 5-HT2A receptor is associated with the occurrence of psychotic symptoms in AD. On the contrary, the serotonin transporter does not appear to be a major susceptibility factor in the pathophysiology of the disease.

Imaging of the 5-HT2A system: age-, gender-, and Alzheimer's disease-related findings

Serotonin (5-HT) and more specifically the 5-HT(2A) receptor is involved in cognitive and non-cognitive behavior and plays an important role in Alzheimer's disease (AD). The objective was to assess the 5-HT(2A) binding potential (BP) in healthy volunteers and AD with SPECT and 123I-5-I-R91150, a selective radio-iodinated 5-HT(2A) receptor antagonist. Twenty-six controls and nine AD patients were included. A semiquantitive analysis with normalization on cerebellar uptake provided estimates of BP for 26 cortical regions of interest. An age-related decline of neocortical BP was found (11.6% per decade). Compared to age-matched controls, a generally decreased neocortical BP in AD was found with a significant regional reduction in the orbitofrontal, prefrontal, lateral frontal, cingulate, sensorimotor, parietal inferior, and occipital region. These results are in line with previous postmortem, in vitro, and PET findings. The age-related decline highlights the necessity for matched advanced age study samples. The fact that the 5-HT(2A) receptor is differentially affected in AD patients has implications for both the etiological basis and therapeutic management of AD.

Neuropsychiatric symptoms in the dementias

PURPOSE OF REVIEW

Neuropsychiatric, or non-cognitive symptoms are increasingly recognized as manifestations of dementias.

RECENT FINDINGS

In Alzheimer's disease, recent advances have included the identification of behavioral profiles, differentiation of apathy and depression, characterization of risk factors for psychosis and its links to agitation and aggression, and an analysis of depressive symptoms in the absence of major depression. Functional neuroimaging data mainly supported the role of the anterior cingulate in apathy. The orbitofrontal and anterior cingulate tangle burden were associated with agitation, and increased orbitofrontal and mid-temporal muscarinic M2 receptors with psychosis and hallucinations. Selected genetic polymorphisms of dopamine and serotonin receptors or transporters were linked with aggression, hallucinations or psychosis. When compared with other dementias, individuals with frontotemporal dementia disclosed, as expected, different behaviors and particularly aberrant social behavior. The frequency of delusions and visual hallucinations was increased in Parkinson's disease, Parkinson's disease with dementia, and dementia with Lewy bodies, suggesting common mechanisms such as Lewy body pathology and cholinergic deficiency. The latter was supported by an improvement of these symptoms by cholinesterase inhibitors.

SUMMARY

Future research directions include both clinical and basic neuroscience investigations. The detection of early neuropsychiatric symptoms might be a marker for dementia, and the possible existence of a mild neuropsychiatric impairment syndrome should be explored. More longitudinal studies with pathological confirmation will facilitate correlations with neuropsychiatric symptoms. Functional neuroimaging and behavioral neurogenetics will permit in-vivo correlations and consequently help patient management and care.