Higher prevalence of dementia in patients with schizophrenia: A nationwide population-based study

Genetic overlap between schizophrenia spectrum disorders and Alzheimer's disease: Current evidence and future directions - An integrative review

Schizophrenia and Alzheimer's disease (AD) are distinct neurodegenerative disorders characterized by progressive cognitive deficits and structural alterations in the brain. Schizophrenia typically emerges in adolescence or early adulthood with symptoms such as hallucinations, delusions, and cognitive impairments, whereas AD primarily affects elderly individuals, causing progressive memory loss, cognitive decline, and behavioral changes. Delusional disorder, which often emerges later in life, shares some features with schizophrenia and is considered a schizophrenia spectrum disorder. Patients with schizophrenia or delusional disorder, particularly women and those aged 65 years or older, have an increased risk of developing AD later in life. In contrast, approximately 30 % of AD patients exhibit psychotic symptoms, which accelerate cognitive decline and worsen health outcomes. This integrative review explored the genetic overlap between schizophrenia spectrum disorders and AD to identify potential shared genetic factors. The genetic correlations between schizophrenia and AD were weak but positive (rg=0.03-0.10). Polygenic risk scores (PRSs) for schizophrenia and AD indicate some genetic predisposition, although findings are inconsistent among studies; e.g., PRS-schizophrenia or PRS-AD were associated with the risk of developing psychosis in patients with AD. A higher PRS for various developmental and psychiatric disorders was correlated with an earlier age at onset of schizophrenia. Research gaps include the need for studies on the impacts of PRS-AD on the risk of schizophrenia, genetic correlations between later-onset delusional disorder and AD, and genetic relationships between AD and late-onset schizophrenia (LOS) with a greater risk of progressing to AD. Further investigation into these genetic overlaps is crucial to enhance prevention, treatment, and prognosis for affected patients.

Biomarkers of neurodegeneration in schizophrenia: systematic review and meta-analysis

QUESTION

Does neurodegenerative disease underlie the increased rate of dementia observed in older people with schizophrenia? Several studies have reported a higher prevalence of dementia in people with schizophrenia compared with the general population. This may reflect a higher risk of developing neurodegenerative diseases such as vascular dementia or Alzheimer's disease (AD). Alternatively, this may reflect non-pathological, age-related cognitive decline in a population with low cognitive reserve.

STUDY SELECTION AND ANALYSIS

We reviewed papers that compared postmortem findings, hippocampal MRI volume or cerebrospinal fluid (CSF) markers of AD, between patients with schizophrenia with evidence of cognitive impairment (age ≥45 years) with controls. We subsequently performed a meta-analysis of postmortem studies that compared amyloid-β plaques (APs) or neurofibrillary tangles (NFTs) in cognitively impaired patients with schizophrenia to normal controls or an AD group.

FINDINGS

No studies found a significant increase of APs or NFTs in cognitively impaired patients with schizophrenia compared with controls. All postmortem studies that compared APs or NFTs in patients with schizophrenia to an AD group found significantly more APs or NFTs in AD. No studies found a significant differences in CSF total tau or phosphorylated tau between patients with schizophrenia and controls. The two studies which compared CSF Aβ42 between patients with schizophrenia and controls found significantly decreased CSF Aβ42 in schizophrenia compared with controls. Hippocampal volume findings were mixed.

CONCLUSIONS

Studies have not found higher rates of AD-related pathology in cognitively impaired individuals with schizophrenia compared with controls. Higher rates of dementia identified in population studies may reflect a lack of specificity in clinical diagnostic tools used to diagnose dementia.

Integrating Electronic Health Records and Polygenic Risk to Identify Genetically Unrelated Comorbidities of Schizophrenia That May Be Modifiable

Background

Patients with schizophrenia have substantial comorbidity that contributes to reduced life expectancy of 10 to 20 years. Identifying modifiable comorbidities could improve rates of premature mortality. Conditions that frequently co-occur but lack shared genetic risk with schizophrenia are more likely to be products of treatment, behavior, or environmental factors and therefore are enriched for potentially modifiable associations.

Methods

Phenome-wide comorbidity was calculated from electronic health records of 250,000 patients across 2 independent health care institutions (Vanderbilt University Medical Center and Mass General Brigham); associations with schizophrenia polygenic risk scores were calculated across the same phenotypes in linked biobanks.

Results

Schizophrenia comorbidity was significantly correlated across institutions (r = 0.85), and the 77 identified comorbidities were consistent with prior literature. Overall, comorbidity and polygenic risk score associations were significantly correlated (r = 0.55, p = 1.29 × 10-118). However, directly testing for the absence of genetic effects identified 36 comorbidities that had significantly equivalent schizophrenia polygenic risk score distributions between cases and controls. This set included phenotypes known to be consequences of antipsychotic medications (e.g., movement disorders) or of the disease such as reduced hygiene (e.g., diseases of the nail), thereby validating the approach. It also highlighted phenotypes with less clear causal relationships and minimal genetic effects such as tobacco use disorder and diabetes.

Conclusions

This work demonstrates the consistency and robustness of electronic health record-based schizophrenia comorbidities across independent institutions and with the existing literature. It identifies known and novel comorbidities with an absence of shared genetic risk, indicating other causes that may be modifiable and where further study of causal pathways could improve outcomes for patients.

Neuropathological substrate of incident dementia in older patients with schizophrenia: A clinicopathological study

AIM

Clinical studies reported that patients with schizophrenia are at a higher risk of developing dementia than people without schizophrenia. However, early neuropathological studies have shown that the incidence of Alzheimer's disease (AD) in schizophrenia patients does not differ from that in controls. These inconsistent results may be attributable to the inclusion of non-AD dementia, but there have been few clinicopathological studies in older patients with schizophrenia based on the current neuropathological classification. This study aimed to investigate the neuropathological basis of incident dementia in older patients with schizophrenia.

METHODS

We systematically examined 32 brains of old patients with schizophrenia using standardized pathological methods. The severity of dementia-related neuropathologies was analyzed using standardized semiquantitative assessments. After excluding patients who fulfilled the neuropathological criteria, clinicopathological variables were compared between patients with and without incident dementia to identify potential differences.

RESULTS

Seven patients fulfilled the pathological criteria for AD (n = 3), argyrophilic grain disease (AGD) (n = 2), dementia with Lewy bodies (n = 1), and AGD/progressive supranuclear palsy (n = 1). Among 25 patients for whom a neuropathological diagnosis was not obtained, 10 had dementia, but the clinicopathological findings did not differ from the remaining 15 patients without dementia.

CONCLUSION

Two types of older schizophrenia patient present dementia: patients with co-existing neurodegenerative disease and patients who do not meet pathological criteria based on the current classification. To understand the neurobiological aspects of incident dementia in older patients with schizophrenia, further clinicopathological studies are needed that do not simply analyze incident dementia as a comorbidity of conventional dementia-related neuropathologies.

BACE1-dependent metabolism of neuregulin 1: Bridging the gap in explaining the occurrence of schizophrenia-like symptoms in Alzheimer's disease with psychosis?

Alzheimer's disease is a neurodegenerative disease mainly characterized by cortico-neuronal atrophy, impaired memory and other cognitive declines. On the other hand, schizophrenia is a neuro-developmental disorder with an overtly active central nervous system pruning system resulting into abrupt connections with common symptoms including disorganised thoughts, hallucination and delusion. Nevertheless, the fronto-temporal anomaly presents itself as a common denominator for the two pathologies. There is even a strong presumption of increased risk of developing co-morbid dementia for schizophrenic individuals and psychosis for Alzheimer's disease patients, overall leading to a further deteriorated quality of life. However, convincing proofs of how these two disorders, although very distant from each other when considering their aetiology, develop coexisting symptoms is yet to be resolved. At the molecular level, the two primarily neuronal proteins β-amyloid precursor protein and neuregulin 1 have been considered in this relevant context, although the conclusions are for the moment only hypotheses. In order to propose a model for explaining the psychotic schizophrenia-like symptoms that sometimes accompany AD-associated dementia, this review projects out on the similar sensitivity shared by these two proteins regarding their metabolism by the β-site APP cleaving enzyme 1.

Psychiatric polygenic risk as a predictor of COVID-19 risk and severity: insight into the genetic overlap between schizophrenia and COVID-19

Despite the high contagion and mortality rates that have accompanied the coronavirus disease-19 (COVID-19) pandemic, the clinical presentation of the syndrome varies greatly from one individual to another. Potential host factors that accompany greater risk from COVID-19 have been sought and schizophrenia (SCZ) patients seem to present more severe COVID-19 than control counterparts, with certain gene expression similarities between psychiatric and COVID-19 patients reported. We used summary statistics from the last SCZ, bipolar disorder (BD), and depression (DEP) meta-analyses available on the Psychiatric Genomics Consortium webpage to calculate polygenic risk scores (PRSs) for a target sample of 11,977 COVID-19 cases and 5943 subjects with unknown COVID-19 status. Linkage disequilibrium score (LDSC) regression analysis was performed when positive associations were obtained from the PRS analysis. The SCZ PRS was a significant predictor in the case/control, symptomatic/asymptomatic, and hospitalization/no hospitalization analyses in the total and female samples; and of symptomatic/asymptomatic status in men. No significant associations were found for the BD or DEP PRS or in the LDSC regression analysis. SNP-based genetic risk for SCZ, but not for BD or DEP, may be associated with higher risk of SARS-CoV-2 infection and COVID-19 severity, especially among women; however, predictive accuracy barely exceeded chance level. We believe that the inclusion of sexual loci and rare variations in the analysis of genomic overlap between SCZ and COVID-19 will help to elucidate the genetic commonalities between these conditions.

Identifying modifiable comorbidities of schizophrenia by integrating electronic health records and polygenic risk

Patients with schizophrenia have substantial comorbidity contributing to reduced life expectancy of 10-20 years. Identifying which comorbidities might be modifiable could improve rates of premature mortality in this population. We hypothesize that conditions that frequently co-occur but lack shared genetic risk with schizophrenia are more likely to be products of treatment, behavior, or environmental factors and therefore potentially modifiable. To test this hypothesis, we calculated phenome-wide comorbidity from electronic health records (EHR) in 250,000 patients in each of two independent health care institutions (Vanderbilt University Medical Center and Mass General Brigham) and association with schizophrenia polygenic risk scores (PRS) across the same phenotypes (phecodes) in linked biobanks. Comorbidity with schizophrenia was significantly correlated across institutions (r = 0.85) and consistent with prior literature. After multiple test correction, there were 77 significant phecodes comorbid with schizophrenia. Overall, comorbidity and PRS association were highly correlated (r = 0.55, p = 1.29×10-118), however, 36 of the EHR identified comorbidities had significantly equivalent schizophrenia PRS distributions between cases and controls. Fifteen of these lacked any PRS association and were enriched for phenotypes known to be side effects of antipsychotic medications (e.g., "movement disorders", "convulsions", "tachycardia") or other schizophrenia related factors such as from smoking ("bronchitis") or reduced hygiene (e.g., "diseases of the nail") highlighting the validity of this approach. Other phenotypes implicated by this approach where the contribution from shared common genetic risk with schizophrenia was minimal included tobacco use disorder, diabetes, and dementia. This work demonstrates the consistency and robustness of EHR-based schizophrenia comorbidities across independent institutions and with the existing literature. It identifies comorbidities with an absence of shared genetic risk indicating other causes that might be more modifiable and where further study of causal pathways could improve outcomes for patients.

Dementia among older people with schizophrenia: an update on recent studies

PURPOSE OF REVIEW

This narrative review examines recently published research that examines the prevalence, underlying causes, and treatments for dementia among people with schizophrenia.

RECENT FINDINGS

People with schizophrenia have high rates of dementia, compared with the general population, and cognitive decline has been observed 14 years prior to onset of psychosis with accelerated decline in middle age. Underlying mechanisms of cognitive decline in schizophrenia include low cognitive reserve, accelerated cognitive aging, cerebrovascular disease and medication exposure. Although pharmacologic, psychosocial and lifestyle interventions show early promise for preventing and mitigating cognitive decline, few studies have been conducted in older people with schizophrenia.

SUMMARY

Recent evidence supports accelerated cognitive decline and brain changes in middle-aged and older people with schizophrenia, relative to the general population. More research in older people with schizophrenia is needed to tailor existing cognitive interventions and develop novel approaches for this vulnerable and high-risk group.

Systematic evaluation of the associations between mental disorders and dementia: An umbrella review of systematic reviews and meta-analyses

BACKGROUND

Increasing evidence support the correlation between mental disorders and the likelihood of developing dementia. We aim to conduct an umbrella review to assess the risk of dementia in patients with eight mental disorders.

METHODS

We searched PubMed, Embase, Web of science, CNKI, VIP, and Wanfang databases from inception to October 29, 2021. For each included meta-analysis, the effect size with a 95% confidence interval was estimated using either a random effect model or a fixed effect model, and between-study heterogeneity was expressed by I² and Cochran's Q test. The ROBIS tool was used to assess the risk of bias.

RESULTS

A total of ten systematic reviews were included. Among these studies, we identified seven risk factors, including anxiety disorder, bipolar disorder, depression, late-life depression, post-traumatic stress disorder, schizophrenia, and sleep disorder. Light to moderate alcohol drinking was identified as a protective factor. The evaluation results of the ROBIS tool showed that nine systematic reviews had high risk of bias and one had low risk of bias. The strength of evidence supporting the associations between late-life depression and all-cause dementia, Alzheimer's disease, and vascular dementia was high; the strength of evidence supporting the association between depression and all-cause dementia was moderate.

LIMITATIONS

Most associations had low strength of evidence and high risk of bias.

CONCLUSIONS

This umbrella review shows that high and moderate evidence supports the associations between some mental disorders and dementia. More cohort studies are needed to support the associations between mental disorders and dementia.

Novel disease associations with schizophrenia genetic risk revealed in ~400,000 UK Biobank participants

Schizophrenia is a serious mental disorder with considerable somatic and psychiatric morbidity. It is unclear whether comorbid health conditions predominantly arise due to shared genetic risk or consequent to having schizophrenia. To explore the contribution of genetic risk for schizophrenia, we analysed the effect of schizophrenia polygenic risk scores (PRS) on a broad range of health problems in 406 929 individuals with no schizophrenia diagnosis from the UK Biobank. Diagnoses were derived from linked health data including primary care, hospital inpatient records, and registers with information on cancer and deaths. Schizophrenia PRS were generated and tested for associations with general health conditions, 16 ICD10 main chapters, and 603 diseases using linear and logistic regressions. Higher schizophrenia PRS was significantly associated with poorer overall health ratings, more hospital inpatient diagnoses, and more unique illnesses. It was also significantly positively associated with 4 ICD10 chapters: mental disorders; respiratory diseases; digestive diseases; and pregnancy, childbirth and the puerperium, but negatively associated with musculoskeletal disorders. Thirty-one specific phenotypes were significantly associated with schizophrenia PRS, and the 19 novel findings include several musculoskeletal diseases, respiratory diseases, digestive diseases, varicose veins, pituitary hyperfunction, and other peripheral nerve disorders. These findings extend knowledge of the pleiotropic effect of genetic risk for schizophrenia and offer insight into how some conditions often comorbid with schizophrenia arise. Additional studies incorporating the genetic basis of hormone regulation and involvement of immune mechanisms in the pathophysiology of schizophrenia may further elucidate the biological mechanisms underlying schizophrenia and its comorbid conditions.

Risk of dementia and death in very-late-onset schizophrenia-like psychosis: A national cohort study

Knowledge is limited regarding the risks of death and dementia in very-late onset schizophrenia-like psychosis (VLOS). This study aims to scrutinize the associations between VLOS with the risks of death and dementia. Based on a prospective Israeli cohort study with national coverage, 94,120 persons without dementia or schizophrenia diagnoses aged 60 to 90 in 2012 were followed-up for the risks of dementia or death from 2013 to 2017. VLOS was classified as present from the age of the first ICD-9 diagnosis during follow-up, otherwise as absent. Hazard ratios (HR) with confidence intervals (95% CI) were computed with survival models to quantify the associations between VLOS and the risks of death and dementia, without and with adjustment for confounding. Nine sensitivity analyses were computed to examine the robustness of the results. The group with VLOS, compared to the group without, had higher death (n = 61, 18.5% vs. n = 7028, 7.5%, respectively) and dementia (n = 64, 19.5% vs. n = 5962, 6.4%, respectively) rates. In the primary analysis, the group with VLOS compared to the group without had increased risks of death (unadjusted HR = 3.10, 95% CI = 2.36, 4.06, P < .001; adjusted HR = 2.89, 95% CI = 2.15, 3.89; P < .001) and dementia (unadjusted HR = 3.81, 95% CI = 2.90, 4.99, P < .001; adjusted HR = 2.67, 95% CI = 1.82, 3.91; P < .001). The results remained statistically significant (P < .05) in all sensitivity analyses, including among persons without antipsychotic medication. The results may support notions of increased dementia risk and accelerated aging in VLOS, or that VLOS is a prodromal state of dementia.

Sex differences in DEK expression in the anterior cingulate cortex and its association with dementia severity in schizophrenia

DEK is a chromatin-remodeling phosphoprotein found in most human tissues, but its expression and function in the human brain is largely unknown. DEK depletion in vitro induces cellular and molecular anomalies associated with cognitive impairment, including down-regulation of the canonical Wnt/β-catenin signaling pathway. ToppGene analyses link DEK loss to genes associated with various dementias and age-related cognitive decline. To examine the role of DEK in cognitive impairment in severe mental illness, DEK protein expression was assayed by immunoblot in the anterior cingulate cortex (ACC) of subjects with schizophrenia. Cognitive impairment is a core feature of schizophrenia and cognitive function in subjects was assessed antemortem using the clinical dementia rating (CDR) scale. DEK protein expression was not significantly altered in schizophrenia (n = 20) compared to control subjects (n = 20). Further analysis revealed significant reduction in DEK protein expression in women with schizophrenia, and a significant increase in expression in men with schizophrenia, relative to their same-sex controls. DEK protein expression levels were inversely correlated with dementia severity in women. Conversely, in men, DEK protein expression and dementia severity were positively correlated. Notably, there was no sex difference in DEK protein expression in the control group, suggesting that this sex difference is specific to schizophrenia and not due to inherent differences in DEK expression between males and females. These results suggest a novel, sex-specific role for DEK in cognitive performance and highlight a putative sex-specific link between central nervous system DEK protein expression and a neuropsychiatric disease that is commonly associated with cognitive impairment.

Schizophrenia and risk of dementia: a meta-analysis study

BACKGROUND

Evidence suggests that schizophrenia may be associated with an increased risk of dementia, but results from prior studies have been inconsistent. This study aimed to estimate the relationship between schizophrenia and incident dementia using a quantitative meta-analysis.

METHODS

Several databases were used to gather relevant information, including PubMed, Embase, and Web of Science, with the publication date of articles limited up to December 23, 2017. All studies reported a multivariate-adjusted estimate, represented as relative risk (RR) with 95% confidence intervals (CIs), for the association between schizophrenia and risk of dementia incidence. Pooled RRs were calculated using a random-effects model.

RESULTS

Six studies met our inclusion criteria for this meta-analysis, which included 206,694 cases of dementia and 5,063,316 participants. All individuals were without dementia at baseline. Overall, the quantitative meta-analysis suggested that subjects with schizophrenia were associated with a significantly greater risk of dementia incidence (RR 2.29; 95% CI 1.35-3.88) than those without.

CONCLUSION

The results of this meta-analysis indicate that individuals with schizophrenia may have an increased risk for the development of dementia. Future studies should explore whether schizophrenia is a modifiable risk factor for dementia.