Systematic reviews of factors associated with the onset and progression of neurological conditions in humans: A methodological overview

Toxic Damage to Motor Neurons

Abstract—Amyotrophic lateral sclerosis (ALS) is a multifactor disease in the development of which both genetic and environmental factors play a role. Specifically, the effects of organic and inorganic toxic substances can result in an increased risk of ALS development and the acceleration of disease progression. It was described that some toxins can induce potentially curable ALS-like syndromes. In this case, the specific treatment for the prevention of the effects of the toxic factor may result in positive clinical dynamics. In this article, we review the main types of toxins that can damage motor neurons in the brain and spinal cord leading to the development of the clinical manifestation of ALS, briefly present historical data on studies on the role of toxic substances, and describe the main mechanisms of the pathogenesis of motor neuron disease associated with their action.

Non-genetic risk and protective factors and biomarkers for neurological disorders: a meta-umbrella systematic review of umbrella reviews

BACKGROUND

The etiologies of chronic neurological diseases, which heavily contribute to global disease burden, remain far from elucidated. Despite available umbrella reviews on single contributing factors or diseases, no study has systematically captured non-purely genetic risk and/or protective factors for chronic neurological diseases.

METHODS

We performed a systematic analysis of umbrella reviews (meta-umbrella) published until September 20th, 2018, using broad search terms in MEDLINE, SCOPUS, Web of Science, Cochrane Database of Systematic Reviews, Cumulative Index to Nursing and Allied Health Literature, ProQuest Dissertations & Theses, JBI Database of Systematic Reviews and Implementation Reports, DARE, and PROSPERO. The PRISMA guidelines were followed for this study. Reference lists of the identified umbrella reviews were also screened, and the methodological details were assessed using the AMSTAR tool. For each non-purely genetic factor association, random effects summary effect size, 95% confidence and prediction intervals, and significance and heterogeneity levels facilitated the assessment of the credibility of the epidemiological evidence identified.

RESULTS

We identified 2797 potentially relevant reviews, and 14 umbrella reviews (203 unique meta-analyses) were eligible. The median number of primary studies per meta-analysis was 7 (interquartile range (IQR) 7) and that of participants was 8873 (IQR 36,394). The search yielded 115 distinctly named non-genetic risk and protective factors with a significant association, with various strengths of evidence. Mediterranean diet was associated with lower risk of dementia, Alzheimer disease (AD), cognitive impairment, stroke, and neurodegenerative diseases in general. In Parkinson disease (PD) and AD/dementia, coffee consumption, and physical activity were protective factors. Low serum uric acid levels were associated with increased risk of PD. Smoking was associated with elevated risk of multiple sclerosis and dementia but lower risk of PD, while hypertension was associated with lower risk of PD but higher risk of dementia. Chronic occupational exposure to lead was associated with higher risk of amyotrophic lateral sclerosis. Late-life depression was associated with higher risk of AD and any form of dementia.

CONCLUSIONS

We identified several non-genetic risk and protective factors for various neurological diseases relevant to preventive clinical neurology, health policy, and lifestyle counseling. Our findings could offer new perspectives in secondary research (meta-research).

Critical review of the association between perineal use of talc powder and risk of ovarian cancer

Over the past four decades, there has been increasing concern that perineal use of talc powder, a commonly used personal care product, might be associated with an increased risk of ovarian cancer.

OBJECTIVES

To critically review all available human epidemiological data on the relationship between perineal use of talc powder and ovarian cancer, with consideration of other relevant experimental evidence.

METHODOLOGY

We identified 30 human studies for qualitative assessment of evidence, including 27 that were retained for further quantitative analysis.

RESULTS

A positive association between perineal use of talc powder and ovarian cancer was found [OR: 1.28 (95% CI: 1.20-1.37)]. A significant risk was noted in Hispanics and Whites, in women applying talc to underwear, in pre-menopausal women and in post-menopausal women receiving hormonal therapy. A negative association was noted with tubal ligation.

CONCLUSION

Perineal use of talc powder is a possible cause of human ovarian cancer.

Most systematic reviews of high methodological quality on psoriasis interventions are classified as high risk of bias using ROBIS tool

OBJECTIVES

No gold standard exists to assess methodological quality of systematic reviews (SRs). Although Assessing the Methodological Quality of Systematic Reviews (AMSTAR) is widely accepted for analyzing quality, the ROBIS instrument has recently been developed. This study aimed to compare the capacity of both instruments to capture the quality of SRs concerning psoriasis interventions.

STUDY DESIGN AND SETTING

Systematic literature searches were undertaken on relevant databases. For each review, methodological quality and bias risk were evaluated using the AMSTAR and ROBIS tools. Descriptive and principal component analyses were conducted to describe similarities and discrepancies between both assessment tools.

RESULTS

We classified 139 intervention SRs as displaying high/moderate/low methodological quality and as high/low risk of bias. A high risk of bias was detected for most SRs classified as displaying high or moderate methodological quality by AMSTAR. When comparing ROBIS result profiles, responses to domain 4 signaling questions showed the greatest differences between bias risk assessments, whereas domain 2 items showed the least.

CONCLUSION

When considering SRs published about psoriasis, methodological quality remains suboptimal, and the risk of bias is elevated, even for SRs exhibiting high methodological quality. Furthermore, the AMSTAR and ROBIS tools may be considered as complementary when conducting quality assessment of SRs.

Determinants of neurological disease: Synthesis of systematic reviews

Systematic reviews were conducted to identify risk factors associated with the onset and progression of 14 neurological conditions, prioritized as a component of the National Population Health Study of Neurological Conditions. These systematic reviews provided a basis for evaluating the weight of evidence of evidence for risk factors for the onset and progression of the 14 individual neurological conditions considered. A number of risk factors associated with an increased risk of onset for more than one condition, including exposure to pesticides (associated with an increased risk of AD, amyotrophic lateral sclerosis, brain tumours, and PD; smoking (AD, MS); and infection (MS, Tourette syndrome). Coffee and tea intake was associated with a decreased risk of onset of both dystonia and PD. Further understanding of the etiology of priority neurological conditions will be helpful in focusing future research initiatives and in the development of interventions to reduce the burden associated with neurological conditions in Canada and internationally.

Risk factors for the onset and progression of Huntington disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized by chorea, behavioural and psychiatric manifestations, and dementia, caused by a CAG triplet repeat expansion in the huntingtin gene. Systematic review of the literature was conducted to determine the risk factors for the onset and progression of HD. Multiple databases were searched, using terms specific to Huntington disease and to studies of aetiology, risk, prevention and genetics, limited to studies on human subjects published in English or French between 1950 and 2010. Two reviewers independently screened the abstracts and identified potentially relevant articles for full-text review using predetermined inclusion criteria. Three major categories of risk factors for onset of HD were identified: CAG repeat length in the huntingtin gene, CAG instability, and genetic modifiers. Of these, CAG repeat length in the huntingtin gene is the most important risk factor. For the progression of HD: genetic, demographic, past medical/clinical and environmental risk factors have been studied. Of these factors, genetic factors appear to play the most important role in the progression of HD. Among the potential risk factors, CAG repeat length in the mutant allele was found to be a relatively consistent and significant risk factor for the progression of HD, especially in motor, cognitive, and other neurological symptom deterioration. In addition, there were many consistent results in the literature indicating that a higher number of CAG repeats was associated with shorter survival, faster institutionalization, and earlier percutaneous endoscopic gastrostomy.

A systematic review of the risk factors associated with the onset and progression of primary brain tumours

The overall aim of this systematic review was to identify risk factors for onset and natural progression, which were shown to increase, decrease, or have a null association with risk of primary brain tumour. For onset, the project was separated into two phases. The first phase consisted of a systematic search of existing systematic reviews and meta-analyses. Moderate to high methodological quality reviews were incorporated and summarized with relevant observational studies published since 2010, identified from a systematic search performed in phase 2. For natural progression, only the first phase was conducted. Standard systematic review methodology was utilized. Based on this review, various genetic variants, pesticide exposures, occupational farming/hairdressing, cured meat consumption and personal hair dye use appear to be associated with increased risk of onset amongst adults. The specific EGF polymorphsm 61-A allele within Caucasian populations and having a history of allergy was associated with a decreased risk. For progression, M1B-1 antigen was shown to increase the risk. High birth weight, pesticide exposure (childhood exposure, and parental occupational exposure) and maternal consumption of cured meat during pregnancy may also increase the risk of onset of childhood brain tumours. Conversely, maternal intake of pre-natal supplements (folic acid) appeared to decrease risk. Children with neurofibromatosis 2 were considered to have worse overall and relapse free survival compared to neurofibromatosis 1, as were those children who had grade III tumours compared to lesser grades.

Burden of neurological conditions in Canada

Neurological conditions are among the leading causes of disability in the Canadian population and are associated with a large public health burden. An increase in life expectancy and a declining birth rate has resulted in an aging Canadian population, and the proportion of age-adjusted mortality due to non-communicable diseases has been steadily increasing. These conditions are frequently associated with chronic disability and an increasing burden of care for patients, their families and caregivers. The National Population Health Study of Neurological Conditions (NPHSNC) aims to improve knowledge about neurological conditions and their impacts on individuals, their families, caregivers and health care system. The Systematic Review of Determinants of Neurological Conditions, a specific objective within the NPHSNC, is a compendium of systematic reviews on risk factors affecting onset and progression of the following 14 priority neurological conditions: Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), brain tumours (BT), cerebral palsy (CP), dystonia, epilepsy, Huntington's disease (HD), hydrocephalus, multiple sclerosis (MS), muscular dystrophies (MD), neurotrauma, Parkinson's disease (PD), spina bifida (SB), and Tourette's syndrome (TS). The burden of neurological disease is expected to increase as the population ages, and this trend is presented in greater detail for Alzheimer's and Parkinson's disease because the incidence of these two common neurological diseases increases significantly with age over 65 years. This article provides an overview of burden of neurological diseases in Canada to set the stage for the in-depth systematic reviews of the 14 priority neurological conditions presented in subsequent articles in this issue.

Onset and progression factors in Parkinson's disease: A systematic review

Current research has identified several factors thought to be associated with the onset and progression of Parkinson's Disease (PD); however, whether certain factors contribute to or are protective against PD remains unclear. As such, a systematic search of the literature was performed using variations of MeSH and keyword search terms to identify and summarize systematic reviews and primary studies pertaining to factors associated with the onset and progression of PD. Factors referred to both traditional risk factors and prodromal markers. The following databases were searched: MEDLINE, MEDLINE In-Process, EMBASE, PsycINFO, Scopus, Web of Science, Cochrane Database of Systematic Reviews, Cumulative Index to Nursing and Allied Health Literature (CINAHL), ProQuest Dissertations & Theses, AARP AgeLine, and PDGene. A quality assessment of included systematic reviews was completed using the validated Assessment of the Methodological Quality of Systematic Reviews (AMSTAR) tool. Data extraction targeted reported factors, risk estimates, and 95% confidence intervals (CI). Findings identified 11 systematic reviews of sufficient quality reporting factors for PD onset, and no systematic reviews reporting factors for PD progression. In addition, 93 primary articles were identified, of which, 89 articles addressed factors related to PD onset and 4 articles addressed factors related to the PD progression. Pesticide exposure, rural living, well-water drinking, and farming occupation were consistently found to be positively associated with the onset of PD. Moreover, family history and polymorphisms to key genes were also found to be positively associated with the onset of PD. Conversely, coffee consumption, cigarette smoking, and some polymorphisms were consistently found to be negatively associated with the onset of PD. Urate was the only identified factor linked to the progression of PD; it was mostly found to be negatively associated with PD. In sum, the evidence was systematically found and summarized in the literature pertaining to factors related to the onset and progression of PD.

Factors associated with the onset and progression of neurotrauma: A systematic review of systematic reviews and meta-analyses

Neurotrauma, including traumatic brain injury (TBI) and spinal cord injury (SCI), is a preventable condition that imposes an important burden on the Canadian society. In this study, the current evidence on risk factors for the onset and progression of neurotrauma is systematically reviewed and synthesized. Searches of the Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects (DARE), Medline and Medline in Process (via OVID), EMBASE and PsycINFO from inception to February 2013 were conducted to identify relevant systematic reviews and meta-analyses published in English or French. Two referees screened and assessed the quality of the studies using the AMSTAR tool. Thirty-two studies examined at least one risk factor for the onset of neurotrauma. Thirteen studies passed the quality assessment and the majority evaluated the impact of protective equipment in sports. Helmets effectively reduce TBI from bicycling, skiing, snowboarding, ice hockey and motorcycling. There was no evidence of a protective effect of helmets for SCI. No studies contributed evidence on risk factors for the onset of SCI. Of two studies examining risk factors for the progression of neurotrauma, only injury severity was found to be associated with poorer post-injury outcomes. Substantial evidence supports the use of helmets for the prevention of TBI in sports and motorcycling and face shields in ice hockey. Addressing bicycle helmet legislation across Canada may be an effective option for reducing TBI caused by bicycle accidents. Limited evidence on relevant risk factors for spinal cord injuries and neurotrauma progression was available.