Epidemiology of presenile Alzheimer's disease in Scotland (1974-88) II. Exposures to possible risk factors

Occupational and domestic exposure associations with cerebral small vessel disease and vascular dementia: A systematic review and meta-analysis

INTRODUCTION

The prevalence of cerebral smallvessel disease (SVD) and vascular dementia according to workplace or domestic exposure to hazardous substances is unclear.

METHODS

We included studies assessing occupational and domestic hazards/at-risk occupations and SVD features. We pooled prevalence estimates using random-effects models where possible, or presented a narrative synthesis.

RESULTS

We included 85 studies (n = 47,743, mean age = 44·5 years). 52/85 reported poolable estimates. SVD prevalence in populations exposed to carbon monoxide was 81%(95% CI = 60-93%; n = 1373; results unchanged in meta-regression), carbon disulfide73% (95% CI = 54-87%; n = 131), 1,2-dichloroethane 88% (95% CI = 4-100%, n = 40), toluene 82% (95% CI = 3-100%, n = 64), high altitude 49% (95% CI = 38-60%; n = 164),and diving 24% (95% CI = 5-67%, n = 172). We narratively reviewed vascular dementia studies and contact sport, lead, military, pesticide, and solvent exposures as estimates were too few/varied to pool.

DISCUSSION

SVD and vascular dementia may be associated with occupational/domestic exposure to hazardous substances. CRD42021297800.

Risk Factors for Young-Onset Dementia in the UK Biobank

Importance

There is limited information on modifiable risk factors for young-onset dementia (YOD).

Objective

To examine factors that are associated with the incidence of YOD.

Design, Setting, and Participants

This prospective cohort study used data from the UK Biobank, with baseline assessment between 2006 and 2010 and follow-up until March 31, 2021, for England and Scotland, and February 28, 2018, for Wales. Participants younger than 65 years and without a dementia diagnosis at baseline assessment were included in this study. Participants who were 65 years and older and those with dementia at baseline were excluded. Data were analyzed from May 2022 to April 2023.

Exposures

A total of 39 potential risk factors were identified from systematic reviews of late-onset dementia and YOD risk factors and grouped into domains of sociodemographic factors (education, socioeconomic status, and sex), genetic factors (apolipoprotein E), lifestyle factors (physical activity, alcohol use, alcohol use disorder, smoking, diet, cognitive activity, social isolation, and marriage), environmental factors (nitrogen oxide, particulate matter, pesticide, and diesel), blood marker factors (vitamin D, C-reactive protein, estimated glomerular filtration rate function, and albumin), cardiometabolic factors (stroke, hypertension, diabetes, hypoglycemia, heart disease, atrial fibrillation, and aspirin use), psychiatric factors (depression, anxiety, benzodiazepine use, delirium, and sleep problems), and other factors (traumatic brain injury, rheumatoid arthritis, thyroid dysfunction, hearing impairment, and handgrip strength).

Main Outcome and Measures

Multivariable Cox proportional hazards regression was used to study the association between the risk factors and incidence of YOD. Factors were tested stepwise first within domains and then across domains.

Results

Of 356 052 included participants, 197 036 (55.3%) were women, and the mean (SD) age at baseline was 54.6 (7.0) years. During 2 891 409 person-years of follow-up, 485 incident YOD cases (251 of 485 men [51.8%]) were observed, yielding an incidence rate of 16.8 per 100 000 person-years (95% CI, 15.4-18.3). In the final model, 15 factors were significantly associated with a higher YOD risk, namely lower formal education, lower socioeconomic status, carrying 2 apolipoprotein ε4 allele, no alcohol use, alcohol use disorder, social isolation, vitamin D deficiency, high C-reactive protein levels, lower handgrip strength, hearing impairment, orthostatic hypotension, stroke, diabetes, heart disease, and depression.

Conclusions and Relevance

In this study, several factors, mostly modifiable, were associated with a higher risk of YOD. These modifiable risk factors should be incorporated in future dementia prevention initiatives and raise new therapeutic possibilities for YOD.

Do prenatal factors shape the risk for dementia?: A systematic review of the epidemiological evidence for the prenatal origins of dementia

PURPOSE

Prenatal factors such as maternal stress, infection and nutrition affect fetal brain development and may also influence later risk for dementia. The purpose of this systematic review was to provide an overview of all studies which investigated the association between prenatal factors and later risk for dementia.

METHODS

We systematically searched MEDLINE and Embase for original human studies reporting on associations between prenatal factors and dementia from inception to 23 November 2022. Prenatal factors could be any factor assessed during pregnancy, at birth or postnatally, provided they were indicative of a prenatal exposure. Risk of bias was assessed using the Newcastle Ottawa Scale. We followed PRISMA guidelines for reporting.

RESULTS

A total of 68 studies met eligibility criteria (including millions of individuals), assessing maternal age (N = 30), paternal age (N = 22), birth order (N = 15), season of birth (N = 16), place of birth (N = 13), prenatal influenza pandemic (N = 1) or Chinese famine exposure (N = 1), birth characteristics (N = 3) and prenatal hormone exposure (N = 4). We observed consistent results for birth in a generally less optimal environment (e.g. high infant mortality area) being associated with higher dementia risk. Lower and higher birth weight and prenatal famine exposure were associated with higher dementia risk. The studies on season of birth, digit ratio, prenatal influenza pandemic exposure, parental age and birth order showed inconsistent results and were hampered by relatively high risk of bias.

CONCLUSION

Our findings suggest that some prenatal factors, especially those related to a suboptimal prenatal environment, are associated with an increased dementia risk. As these associations may be confounded by factors such as parental socioeconomic status, more research is needed to examine the potential causal role of the prenatal environment in dementia.

Geographical variation in dementia: systematic review with meta-analysis

BACKGROUND

Geographical variation in dementia prevalence and incidence may indicate important socio-environmental contributions to dementia aetiology. However, previous comparisons have been hampered by combining studies with different methodologies. This review systematically collates and synthesizes studies examining geographical variation in the prevalence and incidence of dementia based on comparisons of studies using identical methodologies.

METHODS

Papers were identified by a comprehensive electronic search of relevant databases, scrutinising the reference sections of identified publications, contacting experts in the field and re-examining papers already known to us. Identified articles were independently reviewed against inclusion/exclusion criteria and considered according to geographical scale. Rural/urban comparisons were meta-analysed.

RESULTS

Twelve thousand five hundred and eighty records were reviewed and 51 articles were included. Dementia prevalence and incidence varies at a number of scales from the national down to small areas, including some evidence of an effect of rural living [prevalence odds ratio (OR) = 1.11, 90% confidence interval (CI) 0.79-1.57; incidence OR = 1.20, 90% CI 0.84-1.71]. However, this association of rurality was stronger for Alzheimer disease, particularly when early life rural living was captured (prevalence OR = 2.22, 90% CI 1.19-4.16; incidence OR = 1.64, 90% CI 1.08-2.50).

CONCLUSIONS

There is evidence of geographical variation in rates of dementia in affluent countries at a variety of geographical scales. Rural living is associated with an increased risk of Alzheimer disease, and there is a suggestion that early life rural living further increases this risk. However, the fact that few studies have been conducted in resource-poor countries limits conclusions.

Spatial distribution and secular trends in the epidemiology of Alzheimer's disease

There are well-established differences in dementia incidence between communities and within communities over time. In part, these differences may be attributable to local improvements in dementia diagnosis and classification. Nevertheless, there are grounds for cautious optimism that there have been slight, but significant, recent reductions in dementia incidence. Possible causes include public health measures to reduce mortality attributable to stroke and heart disease, improved nutrition, and greater personal wealth. A life-course approach to dementia pathophysiology may help to elucidate the nature and timing of interventions that might delay dementia onset.

How the 1932 and 1947 mental surveys of Aberdeen schoolchildren provide a framework to explore the childhood origins of late onset disease and disability

OBJECTIVES

To describe the discovery and development of the Aberdeen 1921 and 1936 birth cohort studies.

STUDY DESIGN

The Aberdeen birth cohort studies were started in 1998 when the Scottish Mental Survey archives of the Scottish Council for Research in Education were re-discovered and permissions granted to follow-up survivors born in 1921 or 1936 and then aged about 77 or 64 years and who had entered (or were about to enter) the age of greatest risk for Alzheimer's disease (AD).

MAIN OUTCOME MEASURES

Sources of attrition from the study, exposures to childhood adversity, nutritional, genetic and life style factors of possible relevance to extent of age-related cognitive decline and the timing of onset of dementia.

RESULTS

By 2010, the feasibility of following up more than 75% of Scottish Mental Survey survivors living in the Aberdeen area without dementia was well-established, dementia ascertainment to age about 88 years was completed in the 1921 birth cohort and was underway in the 1936 born cohort.

CONCLUSION

These databases are available to other bone fide research groups wishing to test specific hypotheses that may either replicate their own findings or make best use of the data collected in the Aberdeen studies.

Advanced paternal age is associated with impaired neurocognitive outcomes during infancy and childhood

BACKGROUND

Advanced paternal age (APA) is associated with an increased risk of neurodevelopmental disorders such as autism and schizophrenia, as well as with dyslexia and reduced intelligence. The aim of this study was to examine the relationship between paternal age and performance on neurocognitive measures during infancy and childhood.

METHODS AND FINDINGS

A sample of singleton children (n = 33,437) was drawn from the US Collaborative Perinatal Project. The outcome measures were assessed at 8 mo, 4 y, and 7 y (Bayley scales, Stanford Binet Intelligence Scale, Graham-Ernhart Block Sort Test, Wechsler Intelligence Scale for Children, Wide Range Achievement Test). The main analyses examined the relationship between neurocognitive measures and paternal or maternal age when adjusted for potential confounding factors. Advanced paternal age showed significant associations with poorer scores on all of the neurocognitive measures apart from the Bayley Motor score. The findings were broadly consistent in direction and effect size at all three ages. In contrast, advanced maternal age was generally associated with better scores on these same measures.

CONCLUSIONS

The offspring of older fathers show subtle impairments on tests of neurocognitive ability during infancy and childhood. In light of secular trends related to delayed fatherhood, the clinical implications and the mechanisms underlying these findings warrant closer scrutiny.

Paternal age and spontaneous abortion

OBJECTIVE

To evaluate the influence of paternal age upon spontaneous abortion.

METHODS

This case-control study of 13,865 women draws on data from women's antenatal or postpartum interviews in the Jerusalem Perinatal Study, a population-based cohort derived from 92,408 births in 1964-1976. Case women (n=1,506) reported spontaneous abortion in the pregnancy preceding the interview; they were compared with women reporting live births in their previous pregnancy (n=12,359). Logistic regression was used to adjust for maternal age, maternal diabetes, maternal smoking, history of spontaneous abortions before the index pregnancy, parity at interview, and interval between the index pregnancy and the interview.

RESULTS

The adjusted odds ratio for spontaneous abortion was 0.59 (95% confidence interval 0.45-0.76, P< .0001) for pregnancies conceived from fathers aged younger than 25 years compared with those from fathers aged 25-29 years. For fathers age 40 years or older the odds ratio for spontaneous abortion was 1.6 (95% confidence interval 1.2-2.0, P=.0003) when compared with the same reference group.

CONCLUSION

Increasing paternal age is significantly associated with spontaneous abortion, independent of maternal age and multiple other factors.

A life-course approach to the aetiology of late-onset dementias

Substantial progress has been made in the understanding of the neurobiology of dementias, but comprehensive causal models are not available. Genetic and environmental factors probably interact to determine vulnerability to the dementias. The life-course approach to age-related diseases, when systematically applied to the dementias, provides opportunities to identify the nature and timing of environmental contributions. We discuss the relevance of the fetal origins of adult disease hypothesis to the dementias. Associations between the dementias (most often described as Alzheimer's disease) and ischaemic heart disease, obesity, hypertension, hyperlipidaemia, and non-insulin-dependent diabetes mellitus are set against associations between dementias and childhood intelligence, low educational attainments, low socioeconomic status, occupation, and lifetime dietary history. Biological mechanisms that explain how fetal development might influence the risk of adult disease may be relevant to many age-related diseases including the dementias and, possibly, to the biology of ageing.

The Impact of Childhood Intelligence on Later Life: Following Up the Scottish Mental Surveys of 1932 and 1947

The Scottish Mental Surveys of 1932 and 1947 collected valid IQ-type test scores for almost everyone born in 1921 and 1936 and attending school on June 1, 1932 (N=89,498) and June 4, 1947 (N=70,805). These surveys are described. This research, using the surveys' data, examined (a) the stability of intelligence differences across the life span, (b) the determinants of cognitive change from childhood to old age, and (c) the impact of childhood intelligence on survival and health in old age. Surviving participants of the Scottish Mental Surveys were tested, and the surveys' data were linked with public and health records. Novel findings on the stability of IQ scores from age 11 to age 80; sex differences in cognitive aging; the dedifferentiation hypothesis of cognitive aging; and the effect of childhood IQ on all-cause and specific mortality, morbidity, and frailty in old age are presented.

Early-onset Alzheimer's disease in Scotland: environmental and familial factors

BACKGROUND

Alzheimer's disease (AD) is a common, complex, age-related disorder in which both genetic and environmental factors are important.

AIMS

To integrate recent studies on genetic and environmental factors in AD into a multi-factorial disease model.

METHOD

Disease models to explain gene-environment interaction in cardiovascular disease are related to observations on AD.

RESULTS

Informative, community-based studies on the genetic epidemiology of AD are rare. Putative risk factors from the Scottish studies include increased paternal age in AD men and coal mining as paternal occupation in both AD and vascular dementia. Migration effects suggest that environmental factors in high-incidence AD areas are important during adult life.

CONCLUSIONS

The studies summarised do not provide sufficient data to support a single comprehensive disease model of gene-environment interaction in AD. Future studies will require very large (> or = 600) sample sizes, molecular genetic analysis, and environmental data that span neurodevelopment and the period between disease onset and appearance of clinical symptoms.

Paternal factors and schizophrenia risk: de novo mutations and imprinting

There is a strong genetic component for schizophrenia risk, but it is unclear how the illness is maintained in the population given the significantly reduced fertility of those with the disorder. One possibility is that new mutations occur in schizophrenia vulnerability genes. If so, then those with schizophrenia may have older fathers, because advancing paternal age is the major source of new mutations in humans. This review describes several neurodevelopmental disorders that have been associated with de novo mutations in the paternal germ line and reviews data linking increased schizophrenia risk with older fathers. Several genetic mechanisms that could explain this association are proposed, including paternal germ line mutations, trinucleotide repeat expansions, and alterations in genetic imprinting in one or several genes involved in neurodevelopment. Animal models may be useful in exploring these and other explanations for the paternal age effect and they may provide a novel approach for gene identification. Finally, it is proposed that environmental exposures of the father, as well as those of the mother and developing fetus, may be relevant to the etiology of schizophrenia.